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Sample records for photoinduced spectral change

  1. Photoinduced spectral changes of photoluminescent gold nanoclusters.

    PubMed

    Matulionytė, Marija; Marcinonytė, Raminta; Rotomskis, Ričardas

    2015-05-01

    Ultrasmall photoluminescent gold nanoclusters (Au NCs), composed of several atoms with sizes up to a few nanometers, have recently stimulated extensive interest. Unique molecule-like behaviors, low toxicity, and facile synthesis make photoluminescent Au NCs a very promising alternative to organic fluorophores and semiconductor quantum dots (QDs) in broad ranges of biomedical applications. However, using gold nanoparticles (Au NPs) for bioimaging might cause their degradation under continuous excitation with UV light, which might result in toxicity. We report spectral changes of photoluminescent 2-(N-morpholino) ethanesulfonic acid (MES)-coated (Au-MES) NCs under irradiation with UV/blue light. Photoluminescent water soluble Au- MES NCs with a photoluminescence (PL) band maximum at 476 nm (λex = 420 nm) were synthesized. Under irradiation with 402 nm wavelength light the size of photoluminescent Au-MES NCs decreased (λem = 430 nm). Irradiating the sample solution with 330 nm wavelength light, nonluminescent Au NPs were disrupted, and photoluminescent Au NCs (λem = 476 nm) were formed. Irradiation with 330 nm wavelength light did not directly affect photoluminescent Au-MES NCs, however, increase in PL intensity indicated the formation of photoluminescent Au NCs from the disrupted nonluminescent Au NPs. This study gives a good insight into the photostability of MES-coated Au NPs under continuous excitation with UV/blue light.

  2. Photoinduced spectral changes of photoluminescent gold nanoclusters

    NASA Astrophysics Data System (ADS)

    Matulionytė, Marija; Marcinonytė, Raminta; Rotomskis, Ričardas

    2015-05-01

    Ultrasmall photoluminescent gold nanoclusters (Au NCs), composed of several atoms with sizes up to a few nanometers, have recently stimulated extensive interest. Unique molecule-like behaviors, low toxicity, and facile synthesis make photoluminescent Au NCs a very promising alternative to organic fluorophores and semiconductor quantum dots (QDs) in broad ranges of biomedical applications. However, using gold nanoparticles (Au NPs) for bioimaging might cause their degradation under continuous excitation with UV light, which might result in toxicity. We report spectral changes of photoluminescent 2-(N-morpholino) ethanesulfonic acid (MES)-coated (Au-MES) NCs under irradiation with UV/blue light. Photoluminescent water soluble Au-MES NCs with a photoluminescence (PL) band maximum at 476 nm (λex=420 nm) were synthesized. Under irradiation with 402 nm wavelength light the size of photoluminescent Au-MES NCs decreased (λem=430 nm). Irradiating the sample solution with 330 nm wavelength light, nonluminescent Au NPs were disrupted, and photoluminescent Au NCs (λem=476 nm) were formed. Irradiation with 330 nm wavelength light did not directly affect photoluminescent Au-MES NCs, however, increase in PL intensity indicated the formation of photoluminescent Au NCs from the disrupted nonluminescent Au NPs. This study gives a good insight into the photostability of MES-coated Au NPs under continuous excitation with UV/blue light.

  3. Photoinduced structural changes to protein kinase A

    NASA Astrophysics Data System (ADS)

    Rozinek, Sarah C.; Thomas, Robert J.; Brancaleon, Lorenzo

    2014-03-01

    The importance of porphyrins in organisms is underscored by the ubiquitous biological and biochemical functions that are mediated by these compounds and by their potential biomedical and biotechnological applications. Protoporphyrin IX (PPIX) is the precursor to heme and has biomedical applications such as its use as a photosensitizer in phototherapy and photodetection of cancer. Among other applications, our group has demonstrated that low-irradiance exposure to laser irradiation of PPIX, Fe-PPIX, or meso-tetrakis (4-sulfonatophenyl) porphyrin (TSPP) non-covalently docked to a protein causes conformational changes in the polypeptide. Such approach can have remarkable consequences in the study of protein structure/function relationship and can be used to prompt non-native protein properties. Therefore we have investigated protein kinase A (PKA), a more relevant protein model towards the photo-treatment of cancer. PKA's enzymatic functions are regulated by the presence of cyclic adenosine monophosphate for intracellular signal transduction involved in, among other things, stimulation of transcription, tumorigenesis in Carney complex and migration of breast carcinoma cells. Since phosphorylation is a necessary step in some cancers and inflammatory diseases, inhibiting the protein kinase, and therefore phosphorylation, may serve to treat these diseases. Changes in absorption, steady-state fluorescence, and fluorescence lifetime indicate: 1) both TSPP and PPIX non-covalently bind to PKA where they maintain photoreactivity; 2) absorptive photoproduct formation occurs only when PKA is bound to TSPP and irradiated; and 3) PKA undergoes secondary structural changes after irradiation with either porphyrin bound. These photoinduced changes could affect the protein's enzymatic and signaling capabilities.

  4. Measurements of Photo-induced Changes in Conjugated Polymers

    DOE R&D Accomplishments Database

    Seager, C. H.; Sinclair, M. B.; Mc Branch, D.; Heeger, A. J.; Baker, G. L.

    1991-01-01

    We have used the highly sensitive technique of Photothermal Deflection Spectroscopy (PDS) to measure changes in the infrared absorption spectra of MEHPPV, P3HT and Polydiacetylene-4BCMU induced by pumping these polymers with light above the {pi} - {pi}* transition energy. In contrast to previous chopped light transmission measurements of these effects, the PDS technique can directly measure the buildup or decay of the absorption coefficient, {alpha}, on the time scale of second to days. In the case of MEHPPV we observe that the time scale of seconds to days. In the case of MEHPPV we observe that above-gap light causes the appearance of a broad infrared peak in {alpha}, which continues to grow-in hours after the pump light is first applied. For this polymer the general shape of the absorption spectra in the unpumped state mimics the photo-induced changes, suggesting that remnant photo-induced states determine the maximum transparency observed under normal experimental conditions. For P3HT and to a lesser extent, MEHPPV, we also observe irreversible photo-induced absorption components which we tentatively identify with photo-induced oxidation of the polymer matrix.

  5. Photoinduced changes in photosystem II pigments

    NASA Astrophysics Data System (ADS)

    Andreeva, Atanaska S.; Busheva, Mira C.; Stoitchkova, Katerina V.; Tzonova, Iren K.

    2010-11-01

    The photosynthetic apparatus in higher plants performs two seemingly opposing tasks: efficient harvest of sunlight, but also rapid and harmless dissipation of excess light energy as heat to avoid deleterious photodamage. In order to study this process in pigment-protein supercomplexes of photosystem II (PSII), 77 K fluorescence and room temperature resonance Raman (RR) spectroscopy were applied to investigate the changes in structure and spectral properties of the pigments in spinach PSII membranes. The high-light treatment results in a strong quenching of the fluorescence (being largest when the excitation is absorbed by carotenoids) and a red-shift of the main maximum. Decomposition of the fluorescence spectra into four bands revealed intensive quenching of F685 and F695 bands, possible bleaching of chlorophyll a, enhanced extent of light harvesting complexes (LHCII) aggregation and increased energy transfer to aggregated LHCII. The analysis of RR spectra revealed the predominant contribution of ß-carotene (ß-Car) upon 457.8 and 488 nm excitations and lutein (Lut) at 514.5 nm. During prolonged exposure to strong light no significant bleaching of ß-Car and weak photobleaching of Lut is observed. The results will contribute to the efforts to produce more efficient and robust solar cells when exposed to fluctuations in light intensity.

  6. Preparation of diarylethene copolymers and their photoinduced refractive index change

    NASA Astrophysics Data System (ADS)

    Cho, S. Y.; Yoo, M.; Shin, H.-W.; Ahn, K.-H.; Kim, Y.-R.; Kim, E.

    2003-01-01

    Diarylethene copolymers were synthesized from 1-(6 '-vinyl-2 '-methylbenzo[ b]thiophene-3 '-yl)-2-(2 ''-methylbenzo [ b]thiophene-3 ''-yl)hexafluorocyclopentene (VMBTF6) and 1-[6 '-(4 '''-vinylbenzoyl)-2 '-methylbenzo[ b]thiophene-3 '-yl]-2-(2 ''-methylbenzo[ b]thiophene-3 ''-yl)hexafluorocyclopentene (VBMBTF6) via living free radical techniques using stable TEMPO derivatives. The diarylethene content was controlled by the feed ratio of diarylethene derivatives and styrene. Transparent photochromic polymer films were prepared from the diarylethene copolymers with narrow molecular weight dispersion (PD˜1.3) by spin coating method. Photoinduced refractive index changes (Δ nTE) of the polymer films, with 25 mol% of diaryethene content, accompanied by the photochromic change were determined as 0.0009 and 0.0030 for poly(styrene- ran -VMBTF6) and poly(styrene- ran-VBMBTF6), respectively.

  7. Dynamical properties of nucleus boundaries in photoinduced structural change

    NASA Astrophysics Data System (ADS)

    Ishida, Kunio; Nasu, Keiichiro

    2014-01-01

    Dynamics of the boundaries of photoinduced nuclei in electron-phonon systems is theoretically studied. By regarding the spatial distribution of the excited electronic state population as a geometric pattern, we applied the multifractal analysis to it and calculated the temporal behavior of the fractal dimension f(α) as a function of the Lipschitz-Hölder exponent α, which is an appropriate method for understanding the cooperative relaxation process of photoexcited states. We found that the incubation period observed in various types of photoinduced cooperative phenomena corresponds to the formation of embryonic nuclei which is driven by nonadiabatic/adiabatic transition between electronic states during the relaxation of the Franck-Condon state.

  8. The nature of photoinduced changes in the magnetostriction of yttrium-iron garnet single crystals

    SciTech Connect

    Vorob'eva, N. V.

    2011-05-15

    A model of the occurrence of photoinduced changes in linear magnetostriction is proposed based on a complex experimental study of magnetostrictive strains in yttrium-iron garnets Y{sub 3}Fe{sub 5}O{sub 12} with low contents of different impurities. Analytical expressions for calculating the magnetostriction in yttrium-iron garnet single crystals with different types of doping are presented. The correlation of the photoinduced change in the magnetostriction with the crystallographic features of the samples is demonstrated. The changes in the magnetostriction constants are analyzed quantitatively for samples prepared in different ways.

  9. Photo-induced structural changes in Ge-Sb-Se films

    NASA Astrophysics Data System (ADS)

    Lin, Li; Wang, Guoxiang; Shen, Xiang; Dai, Shixun; Xu, Tiefeng; Nie, Qiuhua

    2017-03-01

    Amorphous Ge-Sb-Se thin films have been prepared by the radio-frequency (RF) magnetron co-sputtering deposition technique, and their intrinsic photosensitivity and photo-induced structural changes have been investigated. The results show a crossover from photodarkening (PD) to photobleaching (PB) in the films when the film compositions change from Se-deficient to rich. Further Raman analysis on these as-prepared thin films irradiated with a laser of wavelength 655 nm in every five minutes provides direct evidence of photo-induced structure rearrangements.

  10. Photoinduced refractive index change and absorption bleaching in poly(methylphenylsilane) under varied atmospheres.

    SciTech Connect

    Potter, Barrett George, Jr.; Simmons-Potter, Kelly; Chandra, Haripin; Thomes, William Joseph, Jr.; Jamison, Gregory Marks

    2005-06-01

    Polysilane materials exhibit large photo-induced refractive index changes under low incident optical fluences, making them attractive candidates for applications in which rapid patterning of photonic device structures is desired immediately prior to their use. This agile fabrication strategy for integrated photonics inherently requires that optical exposure, and associated material response, occurs in nonlaboratory environments, motivating the study of environmental conditions on the photoinduced response of the material. The present work examines the impact of atmosphere on the photosensitive response of poly(methylphenylsilane) (PMPS) thin films in terms of both photoinduced absorption change and refractive index modification. Material was subjected to UV light exposure resonant with the lowest energy optical transition associated with the conjugated Si-Si backbone. Exposures were performed in both aerobic and anaerobic atmospheres (oxygen, air, nitrogen, and 5% H{sub 2}/95% N{sub 2}). The results clearly demonstrate that the photosensitive response of this model polysilane material was dramatically affected by local environment, exhibiting a photoinduced refractive index change, when exposed under an oxygen containing atmosphere, that was twice that observed under anaerobic conditions. This effect is discussed in terms of photo-oxidation processes within the polysilane structure and in the context of the need for predictable photosensitive refractive index change in varied photoimprinting environments.

  11. Photo-induced changes in a hybrid amorphous chalcogenide/silica photonic crystal fiber

    SciTech Connect

    Markos, Christos

    2014-01-06

    Photostructural changes in a hybrid photonic crystal fiber with chalcogenide nanofilms inside the inner surface of the cladding holes are experimentally demonstrated. The deposition of the amorphous chalcogenide glass films inside the silica capillaries of the fiber was made by infiltrating the nanocolloidal solution-based As{sub 25}S{sub 75}, while the photoinduced changes were performed by side illuminating the fiber near the bandgap edge of the formed glass nanofilms. The photoinduced effect of the chalcogenide glass directly red-shifts the transmission bandgap position of the fiber as high as ∼20.6 nm at around 1600 nm wavelength, while the maximum bandgap intensity change at ∼1270 nm was −3 dB.

  12. Photoinduced changes in refractive index of nanostructured shungite-containing polyimide systems

    NASA Astrophysics Data System (ADS)

    Kamanina, N. V.; Serov, S. V.; Shurpo, N. A.; Rozhkova, N. N.

    2011-10-01

    Photoinduced changes in the refractive index of a conjugate polyimide (PI) matrix sensitized by shungite carbon nanoparticles have been studied for the first time. The results are compared to the data of previous investigations of the photorefractive properties of PI matrices doped with fullerenes, carbon nanotubes, and quantum dots. The nonlinear refractive index of the proposed material has been determined using the dynamic holography techniques. The position of conjugate polymer materials of this type among the other nonlinear optical systems is considered.

  13. Perovskites for Photovoltaics in the Spotlight: Photoinduced Physical Changes and Their Implications.

    PubMed

    Gottesman, Ronen; Zaban, Arie

    2016-02-16

    Organic-inorganic halide perovskites are in consensus to revolutionize the field of photovoltaics and optoelectronic devices due to their superior optical and electronic properties which are unprecedented in comparison to those of other solution processed semiconductors. These hybrid materials are used as light absorbers and also as charge carriers which makes them very versatile to be implemented and studied in a multitude of fields. Traditionally, the working paradigm in solar cells and optoelectronic devices' characterization has been that the properties of photovoltaic materials remain stable following illumination of varying times and intensities. However, recently there has been a growing number of reports on prolonged illumination-dependent physical changes in perovskite films and perovskite based devices. The changes are reversible and range from structural transformations and differences in optical characteristics, to an increase in optoelectronic properties and physical parameters. In this Account, we review the physical changes in three reported model systems which display changes under prolonged illumination of light intensities of ∼0.01-1 sun. The three systems are (i) a free-standing perovskite film on a glass substrate, (ii) a symmetrical system with nonselective electrical contacts, and (iii) a working perovskite solar cell (either a planar or a porous structure). We examine each model system and discuss its photoinduced physical changes and conclude with the implications on future experimentation design, data analysis, and characterization that involve organic-inorganic halide perovskites illumination. Since hybrid perovskites are considered to be mixed ionic-electronic conductors in nature, ions that migrate in the perovskite under electrical fields can influence its properties. Therefore, an important distinction is made between photoinduced effects and photo and electric field induced effects. Thus, photoinduced effects are designated as

  14. Erasable photoinduced change of carrier density and coherence lengths in oxygen-deficient YBa 2Cu 3O x

    NASA Astrophysics Data System (ADS)

    Göb, W.; Lang, W.; Markowitsch, W.; Schlosser, V.; Kula, W.; Soblewski, Roman

    1995-11-01

    We report on the persistent and erasable photoinduced change of normal-state transport and superconducting properties of oxygen-deficient YBa 2Cu 3O 6.6 thin films. After illumination with white light for several hours at 150K, a decrease of the electrical resistivity, an increase of the number of mobile holes, and a change of the magnetoresistance caused by superconducting order-parameter fluctuations, were observed. From the latter measurement, we find a photoinduced enhancement of the superconducting coherence lengths in both in-plane and out-of-plane directions.

  15. Photoinduced superhydrophilicity: a kinetic study of time dependent photoinduced contact angle changes on TiO2 surfaces.

    PubMed

    Foran, Philip S; Boxall, Colin; Denison, Kieth R

    2012-12-21

    Transparent TiO(2) thin films were prepared on quartz substrates via a reverse micelle, sol-gel, spin-coating technique. The time dependence of the TiO(2) film photoinduced superhydrophilicity (PISH) was measured by goniometric observation of the contact angle, θ, of sessile water drops at the film surfaces. In these measurements, the TiO(2) substrate was illuminated by 315 nm light and drops were sequentially applied at a range of illumination times. Using a model for the wetting of heterogeneous surfaces derived by Israelachvili and Gee, these measurements were used to calculate the time dependence of f(2), the fractional surface coverage of the TiO(2) surface by adventitious contaminating organics (Israelachvili, J. N.; Gee, M. L. Contact angles on chemically heterogeneous surfaces. Langmuir 1989, 5, 288). Extending this model to include a Langmuir-Hinshelwood based kinetic analysis of f(2) as a function of time allowed for calculation of an expected value for θ immediately prior to illumination, that is, at illumination time t = 0. Such expected values of θ at t = 0 were calculated using two possible values of θ(1), the contact angle on a pristine unilluminated homogeneous TiO(2) surface: (i) θ(1) = 4° as suggested by, inter alia, Zubkov et al. (Zubkov, T.; Stahl, D.; Thompson, T. L.; Panayotov, D.; Diwald, O.; Yates, J. T. Ultraviolet Light-Induced Hydrophilicity Effect on TiO(2)(110)(1 × 1). Dominant Role of the Photooxidation of Adsorbed Hydrocarbons Causing Wetting by Water Droplets. J. Phys. Chem. B2005, 109, 15454); and (ii) where θ(1) = 25°, as suggested by Fujishima et al., representative of a more hydrophobic homogeneous TiO(2) surface that reconstructs upon exposure to ultraband gap illumination into a hydrophilic surface where θ(1) → 0° (Fujishima, A.; Zhang, X.; Tryk, D. A. TiO(2) photocatalysis and related surface phenomena Surf. Sci. Rep.2008, 63, 515). Analysis of data from our experiments and from selected literature sources

  16. On the mechanism of photoinduced refractive index changes in phosphosilicate glass

    SciTech Connect

    Larionov, Yu V; Sokolov, V O; Plotnichenko, V G

    2010-05-26

    The photoinduced growth of the refractive index of phosphosilicate glass during Bragg grating inscription and the thermal decay of the grating have a number of unusual features. The observed index variations are interpreted in terms of a new model for photoinduced glass network rearrangement. The model assumes the formation of photoinduced voids (nanopores) in the glass network near point defects. The nanopores may migrate through the network via bond switching when the network is in a 'soft' state. The photoinduced variations in network density lead to index variations. (fibres)

  17. Hot-carrier cooling and photoinduced refractive index changes in organic-inorganic lead halide perovskites

    NASA Astrophysics Data System (ADS)

    Price, Michael B.; Butkus, Justinas; Jellicoe, Tom C.; Sadhanala, Aditya; Briane, Anouk; Halpert, Jonathan E.; Broch, Katharina; Hodgkiss, Justin M.; Friend, Richard H.; Deschler, Felix

    2015-09-01

    Metal-halide perovskites are at the frontier of optoelectronic research due to solution processability and excellent semiconductor properties. Here we use transient absorption spectroscopy to study hot-carrier distributions in CH3NH3PbI3 and quantify key semiconductor parameters. Above bandgap, non-resonant excitation creates quasi-thermalized carrier distributions within 100 fs. During carrier cooling, a sub-bandgap transient absorption signal arises at ~1.6 eV, which is explained by the interplay of bandgap renormalization and hot-carrier distributions. At higher excitation densities, a `phonon bottleneck' substantially slows carrier cooling. This effect indicates a low contribution from inelastic carrier-impurity or phonon-impurity scattering in these polycrystalline materials, which supports high charge-carrier mobilities. Photoinduced reflectivity changes distort the shape of transient absorption spectra and must be included to extract physical constants. Using a simple band-filling model that accounts for these changes, we determine a small effective mass of mr=0.14 mo, which agrees with band structure calculations and high photovoltaic performance.

  18. Hot-carrier cooling and photoinduced refractive index changes in organic-inorganic lead halide perovskites.

    PubMed

    Price, Michael B; Butkus, Justinas; Jellicoe, Tom C; Sadhanala, Aditya; Briane, Anouk; Halpert, Jonathan E; Broch, Katharina; Hodgkiss, Justin M; Friend, Richard H; Deschler, Felix

    2015-09-25

    Metal-halide perovskites are at the frontier of optoelectronic research due to solution processability and excellent semiconductor properties. Here we use transient absorption spectroscopy to study hot-carrier distributions in CH3NH3PbI3 and quantify key semiconductor parameters. Above bandgap, non-resonant excitation creates quasi-thermalized carrier distributions within 100 fs. During carrier cooling, a sub-bandgap transient absorption signal arises at ∼ 1.6 eV, which is explained by the interplay of bandgap renormalization and hot-carrier distributions. At higher excitation densities, a 'phonon bottleneck' substantially slows carrier cooling. This effect indicates a low contribution from inelastic carrier-impurity or phonon-impurity scattering in these polycrystalline materials, which supports high charge-carrier mobilities. Photoinduced reflectivity changes distort the shape of transient absorption spectra and must be included to extract physical constants. Using a simple band-filling model that accounts for these changes, we determine a small effective mass of mr=0.14 mo, which agrees with band structure calculations and high photovoltaic performance.

  19. Hot-carrier cooling and photoinduced refractive index changes in organic–inorganic lead halide perovskites

    PubMed Central

    Price, Michael B.; Butkus, Justinas; Jellicoe, Tom C.; Sadhanala, Aditya; Briane, Anouk; Halpert, Jonathan E.; Broch, Katharina; Hodgkiss, Justin M.; Friend, Richard H.; Deschler, Felix

    2015-01-01

    Metal-halide perovskites are at the frontier of optoelectronic research due to solution processability and excellent semiconductor properties. Here we use transient absorption spectroscopy to study hot-carrier distributions in CH3NH3PbI3 and quantify key semiconductor parameters. Above bandgap, non-resonant excitation creates quasi-thermalized carrier distributions within 100 fs. During carrier cooling, a sub-bandgap transient absorption signal arises at ∼1.6 eV, which is explained by the interplay of bandgap renormalization and hot-carrier distributions. At higher excitation densities, a ‘phonon bottleneck' substantially slows carrier cooling. This effect indicates a low contribution from inelastic carrier-impurity or phonon–impurity scattering in these polycrystalline materials, which supports high charge-carrier mobilities. Photoinduced reflectivity changes distort the shape of transient absorption spectra and must be included to extract physical constants. Using a simple band-filling model that accounts for these changes, we determine a small effective mass of mr=0.14 mo, which agrees with band structure calculations and high photovoltaic performance. PMID:26404048

  20. Nitroxides as redox probes of melanins: dark-induced and photoinduced changes in redox equilibria

    SciTech Connect

    Sarna, T.; Korytowski, W.; Sealy, R.C.

    1985-05-15

    The interaction of nitroxide free radicals and their reduced products (hydroxylamines) with synthetic and natural melanins has been studied. Electron spin resonance spectroscopy was used to measure changes in radical concentration in the dark and during irradiation with visible or uv light. Some reduction of nitroxide occurs in the dark, and is reversible: the nitroxide can be completely regenerated by the one-electron oxidant ferricyanide. The kinetics of the process depend strongly on radical charge and pH. For positively charged nitroxides the rate is much faster than for either neutral or anionic radicals. At pH 10 the rate is about 20 times faster than at pH 5. Oxidation of hydroxylamine also can occur so that a redox equilibrium is established. The equilibrium constant has been estimated for the reaction between a nitroxide and melanin from autoxidation of 3,4-dihydroxyphenylalanine. Results are also dependent upon the type of melanin used and chemical modification (oxidation or reduction) of the melanin. Redox equilibria are altered during irradiation with either visible or uv light. Rapid oxidation of hydroxylamine to nitroxide is apparent, together with a slower reduction of nitroxide. Action spectra for these processes are related to those for melanin radical production and oxygen consumption in nitroxide-free melanin systems. Reduction of nitroxide is inhibited by oxygen, suggesting a competition between nitroxide and oxygen for photoinduced reducing equivalents.

  1. Changes in spectral properties of detached leaves

    NASA Technical Reports Server (NTRS)

    Daughtry, C. S. T.; Biehl, L. L.

    1984-01-01

    If leaf senescence can be delayed for several days without significant changes in spectral properties, then samples of leaves at remote test sites could be prepared and shipped to laboratories to measure spectral properties. The changes in spectral properties of detached leaves were determined. Leaves from red birch and red pine were immersed in water or 0.001 M benzylaminopurine (BAP) and stored in plastic bags in the dark at either 5 or 25 C. Total directional-hemispherical reflectance and transmittance of the adaxial surface of birch leaves were measured over the 400 to 1100 nm wavelength region with a spectroradiometer and integrating sphere. Pine needles were taped together and reflectance of the mat of needles was measured. Spectral properties changed less than 5% of initial values during the first week when leaves were stored at 5 C. Storage at 25 C promoted rapid senescence and large changes in spectral properties. BAP delayed, but did not stop, senescence at 25 C.

  2. Band Structure Simulations of the Photoinduced Changes in the MgB2:Cr Films

    PubMed Central

    Kityk, Iwan V.; Fedorchuk, Anatolii O.; Ozga, Katarzyna; AlZayed, Nasser S.

    2015-01-01

    An approach for description of the photoinduced nonlinear optical effects in the superconducting MgB2:Cr2O3 nanocrystalline film is proposed. It includes the molecular dynamics step-by-step optimization of the two separate crystalline phases. The principal role for the photoinduced nonlinear optical properties plays nanointerface between the two phases. The first modified layers possess a form of slightly modified perfect crystalline structure. The next layer is added to the perfect crystalline structure and the iteration procedure is repeated for the next layer. The total energy here is considered as a varied parameter. To avoid potential jumps on the borders we have carried out additional derivative procedure.

  3. The impact of photo-induced molecular changes of dairy proteins on their ACE-inhibitory peptides and activity.

    PubMed

    Kerkaert, Barbara; Mestdagh, Frédéric; Cucu, Tatiana; Shrestha, Kshitij; Van Camp, John; De Meulenaer, Bruno

    2012-08-01

    Among all dietary proteins, dairy proteins are the most important source of bio-active peptides which can, however, be affected by modifications upon processing and storage. Since it is still unknown to which extent the biological activity of dairy proteins is altered by chemical reactions, this study focuses on the effect of photo-induced molecular changes on the angiotensin I converting enzyme (ACE) inhibitory activity. Milk proteins were dissolved in phosphate buffer containing riboflavin and stored under light at 4 °C for one month during which the molecular changes and the ACE-inhibitory activity were analysed. An increase in the total protein carbonyls and the N-formylkynurenine content was observed, besides a decrease in the free thiol, tryptophan, tyrosine and histidine content. These changes were more severe in caseins compared with whey proteins and resulted moreover in the aggregation of caseins. Due to these photo-induced molecular changes, a significant loss of the ACE-inhibitory activity was observed for casein peptides. A peptide analysis moreover illustrated that the decreased activity was not attributed to a reduced digestibility but to losses of specific ACE-inhibitory peptides. The observed molecular changes, more specifically the degradation of specific amino acids and the casein aggregation, could be assigned as the cause of the altered peptide pattern and as such of the loss in ACE-inhibitory activity.

  4. Solar Spectral Irradiance Changes During Cycle 24

    NASA Technical Reports Server (NTRS)

    Marchenko, Sergey; Deland, Matthew

    2014-01-01

    We use solar spectra obtained by the Ozone Monitoring Instrument (OMI) on board the Aura satellite to detect and follow long-term (years) and short-term (weeks) changes in the solar spectral irradiance (SSI) in the 265-500 nm spectral range. During solar Cycle 24, in the relatively line-free regions the SSI changed by approximately 0.6% +/- 0.2% around 265 nm. These changes gradually diminish to 0.15% +/- 0.20% at 500 nm. All strong spectral lines and blends, with the notable exception of the upper Balmer lines, vary in unison with the solar "continuum." Besides the lines with strong chromospheric components, the most involved species include Fe I blends and all prominent CH, NH, and CN spectral bands. Following the general trend seen in the solar "continuum," the variability of spectral lines also decreases toward longer wavelengths. The long-term solar cycle SSI changes are closely, to within the quoted 0.1%-0.2% uncertainties, matched by the appropriately adjusted short-term SSI variations derived from the 27 day rotational modulation cycles. This further strengthens and broadens the prevailing notion about the general scalability of the UV SSI variability to the emissivity changes in the Mg II 280 nm doublet on timescales from weeks to years. We also detect subtle deviations from this general rule: the prominent spectral lines and blends at lambda approximately or greater than 350 nm show slightly more pronounced 27 day SSI changes when compared to the long-term (years) trends. We merge the solar data from Cycle 21 with the current Cycle 24 OMI and GOME-2 observations and provide normalized SSI variations for the 170-795 nm spectral region.

  5. Photo-induced transformations in 2,2':5',2''-terthiophene thin films on silver.

    PubMed

    Alaverdyan, Yury; Johansson, Patrik; Käll, Mikael

    2006-03-28

    We report on transient photo-induced structural changes of 2,2':5',2''-terthiophene (3T) adsorbed on silver nanoparticles. Surface-enhanced Raman scattering (SERS) data show that the film thickness predetermines the eventual course of these changes. In particular, for high molecular concentrations (thick adsorbate layers), illumination leads to a photoinduced polymerization of the 3T film. For thin layers ( approximately monolayer coverage), the photoinduced spectral evolution is qualitatively different. We interpret the latter process as a cleavage of the terthiophene molecule, resulting in isolated thiophene units. Calculations of excitation energies for 3T + 3Ag+ and 1T + Ag+ revealed visible transitions, while calculated Raman frequencies indicated 1T as a possible photoproduct. As no photoinduced transformations are observed for 3T in the solid or solution phases, it is likely that the processes reported here originate in surface-enhanced charge-transfer between the Ag-surface and the organic adsorbate.

  6. Photo-induced and electrooptic properties of (Pb,La)(Zr,Ti)O{sub 3} films

    SciTech Connect

    Dimos, D.; Warren, W.L.; Tuttle, B.A.

    1993-07-01

    Photo-induced changes in the hysteresis behavior of sol-gel derived Pb(Zr,Ti)O{sub 3} (PZT) and (Pb,La)(Zr,Ti)O{sub 3} (PLZT) films have been characterized. Film photosensitivity has been evaluated with respect to magnitude of effects, time response and spectral dependence. Photo-induced hysteresis changes exhibit a stretched-exponential time dependence, which implies a dispersive mechanism. The spectral dependence is strongly peaked at the band edge ({approximately} 3.4 eV), which indicates that generation of electron-hole pairs in the material is critical. The photo-induced hysteresis changes are reproducible and stable, which indicates that the controlling charge traps are stable. However, improvements in film photosensitivity will be required to develop these materials for optical memory applications.

  7. Polymers for refractive index change in intraocular lenses: a novel approach for photoinduced tuning of focal length

    NASA Astrophysics Data System (ADS)

    Träger, Jens; Kim, Hee-Cheol; Hampp, Norbert

    2006-02-01

    Before an intraocular lens (IOL) is implanted during cataract surgery, biometric data of the patient's eye have to be determined to calculate the thickness and shape of the IOL. In particular the postoperative anterior chamber depth is an important parameter to predict the correct shape of the IOL. This value, however, cannot be measured without significant uncertainities. We present a solution to this problem, describe novel polymers suitable for IOLs which refractive indices can be changed non-invasively in a photo-induced process. The focal length can be modified by about 2 D, which is sufficient to achive ideal acuteness of vision for almost all patients with implanted IOLs. The change in refractive index is accomplished by linking or cleaving bonds between a sufficiently large number of side groups of the polymer main chain in a photoinduced cyloaddition or cycloreversion, respectively. The photochemical reaction can also be triggered by a two-photon process (TPA) using a pulsed laser system, i.e. the energy required for bond breaking is provided by two photons in the visible range. Light in the UV as well as the visible range of the spectrum cannot induce undesired changes of the refractive index owing to the strong UV-absorption of the cornea and photon densities much too low for TPA, respectively. Due to the excellent spatial resolution that can be achieved with two-photon processes not only modification of the refractive index of the entire lens but also selectively in well defined areas is possible enabling the correction for aberrations such as astigmatism.

  8. Photoinduced changes of surface order in coumarin side-chain polymer films used for liquid crystal photoalignment

    SciTech Connect

    Bergmann, G.; Jackson, P.O.; Hogg, J.H.C.; Stirner, T.; O'Neill, M.; Duffy, W.L.; Kelly, S.M.; Clark, G.F.

    2005-08-08

    Specular x-ray reflectivity probes morphological changes in a crosslinkable coumarin photoalignment polymer film resulting from ultraviolet irradiation. An ordered surface layer with density oscillations compatible with planar side-chain alignment is obtained before irradiation. The ordering is enhanced in the early stages of crosslinking. This is attributed to the photoinduced increase of mobility of the side-chains resulting from the creation of free volume by the crosslinking process. The expansion of the thin film confirms that free volume is created. The surface ordering decreases with prolonged ultraviolet irradiation because of increased material viscosity resulting from a high crosslinked density. The implications of surface ordering on liquid crystal photoalignment are discussed.

  9. Photo-induced refractive index change of amorphous tin-doped As{sub 2}S{sub 8} films and its application to strip waveguide fabrication

    SciTech Connect

    Sun, B.; Chen, B. X.; Sui, G. R.; Wang, G. D.; Zou, L. E.; Iso, M.; Hamanaka, H.

    2009-05-01

    The amorphous chalcogenide glass Sn{sub 1}As{sub 20}S{sub 79} is demonstrated to undergo permanent changes in refractive index on irradiation with ultraviolet light. The refractive properties of this material and the effect of annealing at temperatures below the glass transition temperature are investigated in detail. An Sn{sub 1}As{sub 20}S{sub 79} strip waveguide is fabricated using this photoinduced refractive index change, and the device is shown to function as expected with good propagation characteristics for the 632.8 nm guided mode.

  10. ROLE OF SPATIAL RESOLUTION AND SPECTRAL CONTENT IN CHANGE DETECTION.

    USGS Publications Warehouse

    Milazzo, Valerie A.

    1984-01-01

    Summary form only given, as follows. Advancements in remote sensing technology have brought improvements and sophistication to modern remote sensor systems, especially those aboard earth resources satellites. These improvements have considerbly expanded the capabilities of the newer sensor systems, particularly the capability to achieve greatly increased spatial and spectral resolution levels. The debate still lingers, however, over whether future systems should maximize spatial resolution or spectral information, or both. As yet, the high costs and large volumes of data associated with even modest incremental improvements in spatial and spectral content have precluded the design of a single system that attempts to fully optimize both. Thus, the user is faced with having to choose between those systems providing high spatial resolutions but limited spectral information and those which offer a broad range of spectral data but hold spatial resolution to a less than optimum level. In this study, the contribution of both spatial resolution and spectral content to land cover change detection is examined. Ten-meter SPOT simulation imagery is compared with multispectral images acquired by the Thematic Mapper sensor system for use in the visual interpretation and mapping of changes. Several image processing and enhancement techniques are utilized to maximize the spatial and spectral data content offered by each system. Results indicate that when using visual image interpretation techniques to detect change, higher spatial resolutions are generally preferred over increased spectral content.

  11. Multifractal analysis of photoinduced cooperative phenomena

    NASA Astrophysics Data System (ADS)

    Ishida, Kunio; Nasu, Keiichiro

    2008-01-01

    We study the multifractal properties of the geometrical patterns which appear in the initial processes of photoinduced structural change. Employing a model of localized electrons coupled with a single-phonon mode, we calculate the Lipschitz-Hölder exponent α and singularity spectrum f(α) on the distribution of excited electronic states and molecular distortion by using the box-counting method, and discuss the temporal behavior of photoinduced domains.

  12. SAR image change detection using watershed and spectral clustering

    NASA Astrophysics Data System (ADS)

    Niu, Ruican; Jiao, L. C.; Wang, Guiting; Feng, Jie

    2011-12-01

    A new method of change detection in SAR images based on spectral clustering is presented in this paper. Spectral clustering is employed to extract change information from a pair images acquired on the same geographical area at different time. Watershed transform is applied to initially segment the big image into non-overlapped local regions, leading to reduce the complexity. Experiments results and system analysis confirm the effectiveness of the proposed algorithm.

  13. The γ-ray spectral changes in Fermi blazars

    NASA Astrophysics Data System (ADS)

    Yang, Jianghe; Fan, Junhui; Nie, Jianjun; Yang, Rushu; Tuo, Manxian; Zhang, Yuelian

    2017-02-01

    Based upon Fermi 2FGL and 3FGL catalogues, a sample of 842 blazars (hereinto 356 FSRQs, 486 BL Lac objects) is collected to discuss the changes of γ-ray photon spectral indices and brightness from 2FGL to 3FGL blazars. Our results indicate that the distributions of γ-ray photon spectral indices and luminosities between 2FGL and 3FGL have no obvious difference; The photon spectral indices and γ-ray luminosity from 2FGL are closely correlated with that from 3FGL respectively; There are close anti-relations between the change of photon spectral indices and the change of luminosity for FSRQs and BL Lac objects samples and for sub-class samples of HBLs, IBLs and LBLs, which suggests that the spectrum becomes flat when the source becomes bright.

  14. The spectral changes of deforestation in the Brazilian tropical savanna.

    PubMed

    Trancoso, Ralph; Sano, Edson E; Meneses, Paulo R

    2015-01-01

    The Cerrado is a biome in Brazil that is experiencing the most rapid loss in natural vegetation. The objective of this study was to analyze the changes in the spectral response in the red, near infrared (NIR), middle infrared (MIR), and normalized difference vegetation index (NDVI) when native vegetation in the Cerrado is deforested. The test sites were regions of the Cerrado located in the states of Bahia, Minas Gerais, and Mato Grosso. For each region, a pair of Landsat Thematic Mapper (TM) scenes from 2008 (before deforestation) and 2009 (after deforestation) was compared. A set of 1,380 samples of deforested polygons and an equal number of samples of native vegetation have their spectral properties statistically analyzed. The accuracy of deforestation detections was also evaluated using high spatial resolution imagery. Results showed that the spectral data of deforested areas and their corresponding native vegetation were statistically different. The red band showed the highest difference between the reflectance data from deforested areas and native vegetation, while the NIR band showed the lowest difference. A consistent pattern of spectral change when native vegetation in the Cerrado is deforested was identified regardless of the location in the biome. The overall accuracy of deforestation detections was 97.75%. Considering both the marked pattern of spectral changes and the high deforestation detection accuracy, this study suggests that deforestation in Cerrado can be accurately monitored, but a strong seasonal and spatial variability of spectral changes might be expected.

  15. Changes in spectral properties of detached birch leaves

    NASA Technical Reports Server (NTRS)

    Daughtry, C. S. T.; Biehl, L. L.

    1985-01-01

    A study conducted in order to determine the rate of changes in spectral properties of detached leaves and to evaluate the effectiveness of low temperature and cytokinins for delaying the changes, is examined. For five minutes, leaves from red birch are immersed in water or 0.001 M BAP, and then stored in plastic bags in the dark at either 5 or 25 C. Using a spectroradiometer and an integrating sphere, total directional-hemispherical reflectance and transmittance of the adaxial surface of the leaves are measured over the 400-1100 nm wavelength region. The results indicate that for leaves stored at 5 C for one week, the changes in the spectral properties are less than 5 percent of the initial values, whereas storage at 25 C promotes rapid senescence and large changes in the spectral properties. It is shown that low temperature is more effective than BAP in delaying senescence.

  16. Coherent x-ray diffraction imaging of photo-induced structural changes in BiFeO3 nanocrystals

    NASA Astrophysics Data System (ADS)

    Newton, Marcus C.; Parsons, Aaron; Wagner, Ulrich; Rau, Christoph

    2016-09-01

    Multiferroic materials that exhibit coupling between ferroelectric and magnetic properties are of considerable utility for technological applications and are also interesting from a fundamental standpoint. When reduced to the nanoscale, multiferroic materials often display additional functionality that is dominated by interfacial and confinement effects. Bismuth ferrite (BiFeO3) is one such material with room temperature anti-ferromagnetic and ferroelectric ordering. Optical excitation of BiFeO3 crystals results in an elastic structural deformation of the lattice with a fast response on the pico-second time scale. Here we report on dynamic measurements to investigate the structural properties of BiFeO3 nanoscale crystals using laser excitation and three-dimensional Bragg coherent x-ray diffraction imaging. Tensile strain beyond 8 × {10}-2 was observed predominantly at the surface of the nanoscale crystal as evidenced in the reconstructed phase information and was correlated to photo-induced lattice deformation.

  17. Hyperspectral imagery for observing spectral signature change in Aspergillus flavus

    NASA Astrophysics Data System (ADS)

    DiCrispino, Kevin; Yao, Haibo; Hruska, Zuzana; Brabham, Kori; Lewis, David; Beach, Jim; Brown, Robert L.; Cleveland, Thomas E.

    2005-11-01

    Aflatoxin contaminated corn is dangerous for domestic animals when used as feed and cause liver cancer when consumed by human beings. Therefore, the ability to detect A. flavus and its toxic metabolite, aflatoxin, is important. The objective of this study is to measure A. flavus growth using hyperspectral technology and develop spectral signatures for A. flavus. Based on the research group's previous experiments using hyperspectral imaging techniques, it has been confirmed that the spectral signature of A. flavus is unique and readily identifiable against any background or surrounding surface and among other fungal strains. This study focused on observing changes in the A. flavus spectral signature over an eight-day growth period. The study used a visible-near-infrared hyperspectral image system for data acquisition. This image system uses focal plane pushbroom scanning for high spatial and high spectral resolution imaging. Procedures previously developed by the research group were used for image calibration and image processing. The results showed that while A. flavus gradually progressed along the experiment timeline, the day-to-day surface reflectance of A. flavus displayed significant difference in discreet regions of the wavelength spectrum. External disturbance due to environmental changes also altered the growth and subsequently changed the reflectance patterns of A. flavus.

  18. Adaptive optimal spectral range for dynamically changing scene

    NASA Astrophysics Data System (ADS)

    Pinsky, Ephi; Siman-tov, Avihay; Peles, David

    2012-06-01

    A novel multispectral video system that continuously optimizes both its spectral range channels and the exposure time of each channel autonomously, under dynamic scenes, varying from short range-clear scene to long range-poor visibility, is currently being developed. Transparency and contrast of high scattering medium of channels with spectral ranges in the near infrared is superior to the visible channels, particularly to the blue range. Longer wavelength spectral ranges that induce higher contrast are therefore favored. Images of 3 spectral channels are fused and displayed for (pseudo) color visualization, as an integrated high contrast video stream. In addition to the dynamic optimization of the spectral channels, optimal real-time exposure time is adjusted simultaneously and autonomously for each channel. A criterion of maximum average signal, derived dynamically from previous frames of the video stream is used (Patent Application - International Publication Number: WO2009/093110 A2, 30.07.2009). This configuration enables dynamic compatibility with the optimal exposure time of a dynamically changing scene. It also maximizes the signal to noise ratio and compensates each channel for the specified value of daylight reflections and sensors response for each spectral range. A possible implementation is a color video camera based on 4 synchronized, highly responsive, CCD imaging detectors, attached to a 4CCD dichroic prism and combined with a common, color corrected, lens. Principal Components Analysis (PCA) technique is then applied for real time "dimensional collapse" in color space, in order to select and fuse, for clear color visualization, the 3 most significant principal channels out of at least 4 characterized by high contrast and rich details in the image data.

  19. Spectral changes associated with rain on Titan: observations by VIMS

    NASA Astrophysics Data System (ADS)

    Buratti, B. J.; Dalba, P. A.; Barnes, J.; Baines, K. H.; Brown, R. H.; Clark, R. N.; Nicholson, P. D.; Sotin, C.

    2012-04-01

    Titan has an erosional cycle similar to that on the Earth, with solid, liquid, and gaseous methane taking the place of the Earth’s water. Lakes and ponds, drainage and fluvial features, and clouds all suggest that rain is falling on Titan. A darkening event near clouds covering the Huygens landing site, followed by a return to the previous state, strongly suggested rainfall followed by evaporation (Turtle et al., 2011). The Cassini Visual infrared Mapping Spectrometer (VIMS) obtains medium resolution spectra in the 0.35-5.1 μm spectral region, which includes several atmospheric “windows” that offer glimpses of Titan’s surface. The albedo of the surface can be measured in these windows, and some compositional information, including changes through time, can be derived. VIMS observed an area near 15º south latitude and 330º longitude at two separate times: in August 2009 during T61 and in May 2011 during T76. A spectral analysis of this region, including compensation for varying atmospheric path lengths, shows substantial spectral changes in the two and five micron atmospheric windows. A comparison of the changes with that expected from the deposition and later evaporation of liquid methane or another hydrocarbon shows them to be consistent with rain on Titan. Ackowledgements: This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology under contract to the National Aeronautics and Space Administration. Copyright 2012 all rights reserved. References: Turtle, E. P. et al. (2011) Science 331, 1414.

  20. Synthesis fidelity and time-varying spectral change in vowels

    NASA Astrophysics Data System (ADS)

    Assmann, Peter F.; Katz, William F.

    2005-02-01

    Recent studies have shown that synthesized versions of American English vowels are less accurately identified when the natural time-varying spectral changes are eliminated by holding the formant frequencies constant over the duration of the vowel. A limitation of these experiments has been that vowels produced by formant synthesis are generally less accurately identified than the natural vowels after which they are modeled. To overcome this limitation, a high-quality speech analysis-synthesis system (STRAIGHT) was used to synthesize versions of 12 American English vowels spoken by adults and children. Vowels synthesized with STRAIGHT were identified as accurately as the natural versions, in contrast with previous results from our laboratory showing identification rates 9%-12% lower for the same vowels synthesized using the cascade formant model. Consistent with earlier studies, identification accuracy was not reduced when the fundamental frequency was held constant across the vowel. However, elimination of time-varying changes in the spectral envelope using STRAIGHT led to a greater reduction in accuracy (23%) than was previously found with cascade formant synthesis (11%). A statistical pattern recognition model, applied to acoustic measurements of the natural and synthesized vowels, predicted both the higher identification accuracy for vowels synthesized using STRAIGHT compared to formant synthesis, and the greater effects of holding the formant frequencies constant over time with STRAIGHT synthesis. Taken together, the experiment and modeling results suggest that formant estimation errors and incorrect rendering of spectral and temporal cues by cascade formant synthesis contribute to lower identification accuracy and underestimation of the role of time-varying spectral change in vowels. .

  1. Photoinduced Multicomponent Reactions.

    PubMed

    Garbarino, Silvia; Ravelli, Davide; Protti, Stefano; Basso, Andrea

    2016-12-12

    The combination of multicomponent approaches with light-driven processes opens up new scenarios in the area of synthetic organic chemistry, where the need for sustainable, atom- and energy-efficient reactions is increasingly urgent. Photoinduced multicomponent reactions are still in their infancy, but significant developments in this area are expected in the near future.

  2. Influence of π-conjugation structural changes on intramolecular charge transfer and photoinduced electron transfer in donor-π-acceptor dyads.

    PubMed

    Kim, So-Yoen; Cho, Yang-Jin; Lee, Ah-Rang; Son, Ho-Jin; Han, Won-Sik; Cho, Dae Won; Kang, Sang Ook

    2016-12-21

    The influence of π-conjugation structural changes on photoinduced electron transfer (PET) and intramolecular charge transfer (ICT) processes in π-conjugated donor (D)-acceptor (A) dyads (D-π-A) was investigated. Three types of D-π-A dyads were prepared through the modification of the structure of their π-conjugated linker, including D-π-A (1) and D-πtw-A (2) having a twisted π-conjugation, and D-π-Si-π-A (3) with a π-conjugation severed by a Si-atom. In these dyads, carbazole (Cz) and oxadiazole (Oz) moieties act as an electron donor and acceptor, respectively. The emission maxima of dyads 1 and 3 red-shifted with the increase in polarity, which could be attributed to the ICT process. The fluorescence lifetimes of dyads 1 and 3 were 2.64 and 4.29 ns in CH2Cl2, respectively. In contrast, dyad 2 showed dual emission at 350 and 470 nm in CH2Cl2. The emission of dyad 2 at 380 nm corresponded to the monomer fluorescence in the locally excited state. Moreover, the emission at 470 nm increased simultaneously with the diminishing of the fluorescence at 380 nm. This emission band can be assigned as the intramolecular exciplex emission, and showed a strong solvatochromic shift. The low emission quantum yield (<3%) of dyad 2 is due to the PET process. In dyad 2, the cationic and anionic radical species generated by the PET process were confirmed by femtosecond transient absorption (fs-TA) spectroscopy. Upon photoexcitation at 290 or 340 nm, the A or D moieties can be selectively excited. Upon excitation at 290 nm, the acceptor moiety can be excited to the (1)A* state, thus the photoinduced hole transfer (PHT) takes place from (1)A* to D through the HOMO levels within a few picoseconds. On the other hand, when the donor moiety is excited at 340 nm, the PET process occurs from (1)D* to A. Based on the fs-TA studies, it was found that the dynamics and mechanisms for the electron (or charge) transfer were strongly affected by the variation of the π-conjugation of the

  3. Spectral changes in spontaneous MEG activity across the lifespan

    NASA Astrophysics Data System (ADS)

    Gómez, Carlos; Pérez-Macías, Jose M.; Poza, Jesús; Fernández, Alberto; Hornero, Roberto

    2013-12-01

    Objective. The aim of this study is to explore the spectral patterns of spontaneous magnetoencephalography (MEG) activity across the lifespan. Approach. Relative power (RP) in six frequency bands (delta, theta, alpha, beta-1, beta-2 and gamma) was calculated in a sample of 220 healthy subjects with ages ranging from 7 to 84 years. Main results. A significant RP decrease in low-frequency bands (i.e. delta and theta) and a significant increase in high bands (mainly beta-1 and beta-2) were found from childhood to adolescence. This trend was observed until the sixth decade of life, though only slight changes were found. Additionally, healthy aging was characterized by a power increase in low-frequency bands. Our results show that spectral changes across the lifespan may follow a quadratic relationship in delta, theta, alpha, beta-2 and gamma bands with peak ages being reached around the fifth or sixth decade of life. Significance. Our findings provide original insights into the definition of the ‘normal’ behavior of age-related MEG spectral patterns. Furthermore, our study can be useful for the forthcoming MEG research focused on the description of the abnormalities of different brain diseases in comparison to cognitive decline in normal aging.

  4. Photoinduced electron-transfer reactions of 2(3H)-furanones and bis(benzofuranones). Spectral and kinetic behavior of radicals and radical cations

    SciTech Connect

    Davis, H.F.; Lohray, B.B.; Gopidas, K.R.; Kumar, C.V.; Das, P.K.; George, M.V.

    1985-10-04

    The spectral and kinetic behaviors of radical cations produced under efficient electron-transfer quenching of 1,4-dicyanonaphthalene or 9,10-dicyanoanthracene singlet by a number of 2(3H)-furanones and bis(benzo-furanones) have been examined by nanosecond laser flash photolysis (337.1 and 425 nm). The efficiencies of net electron transfer in the course of quenching processes are moderately high (0.2-0.6) in acetonitrile. The radical cations from bis(benzofuranones) several 2(3H)-furanones containing a benzyl group at the 3-position undergo fragmentation to benzofuranoxy and furanoxy radicals (+ benzyl or benzofuranoyl carbocations) with rate constants of 0.3 x 10W s . The long-lived furanoxy radicals, independently generated via hydrogen abstraction by tert-butoxy radicals from 2(5H)-furanones and 3-phenyl-2(3H)-benzofuranone, as well as via direct photolysis of 3-benzoyl-3,5-diphenyl-2(3H)-furanone, are characterized by sharply structured absorption spectra and relatively slow second-order decay kinetics (6-8 x 10Y M s in 1:2 benzene-di-tert butyl peroxide, v/v). 28 references, 7 figures, 3 tables.

  5. Photo-induced changes of the optical constants of chalcodenide Ge19Sb1Te80 films

    NASA Astrophysics Data System (ADS)

    Pamukchieva, Vesela; Szekeres, Anna M.; Todorova, Kalina

    2004-10-01

    In this work a preliminary study of the influence of light illumination on the optical constants of chalcogenide thin films with non-stoichiometric Ge19Sb1Te80 composition is presented. Films of Ge19Sb1Te80 with a thickness of ~1 μm were deposited onto glass substrates by vacuum thermal evaporation of parent glasses. The as-deposited films were exposed to light by using a 500 W HBO mercury lamp. The optical constants of the films, before and after their illumination, were evaluated from the ellipsometric measurements in the spectral range of 300 - 820 nm. It has been established that illumination of the films leads to a decrease of the refractive index in the studied spectral region, while a slight increase of the extinction coefficient in the 600 - 800 nm range is observed. For the given film composition the optical bandgap energy of 0.76 eV reduces to 0.62 eV. The film structure shows a very slow recovery expresed in the increase of bandgap energy towards its initial value. The observed decrease of the bandgap energy after illumination is indicative that the film structure undergoes rearrangements upon exposure to light leading to the effect of photodarkening.

  6. Studies of the spectral signatures of a changing climate

    NASA Astrophysics Data System (ADS)

    Harries, J. E.; Brindley, H. E.

    2008-12-01

    Observations of the outgoing longwave spectrum of the Earth have been made from a number of spacecraft, dating back to the IRIS experiment on Nimbus 4 in 1970. Using these observations, and following very careful calibration exercises, we have searched cloud-cleared (clear sky) spectra , and found changes in the spectral signatures of greenhouse gases such as CO2, CH4, O3 and CFCl3. The OLR spectrum also contains information on feedback processes, such as those due to water vapour (and the water vapour continuum) and clouds. The paper reports on studies of these observations, and on simulations of the spectral signatures, using both model runs and re-analysis data from NCEP and ERA-40. A major problem is that of sampling of the fields, especially of clouds, and this will be discussed. It also transpires that the primary mechanism of water vapour feedback is through emission from the pure rotation band in the far IR. We find that inter-annual variability contributes to changes with time that can either increase or decrease the effectiveness of this feedback. This work contributes to the specification of the CLARREO project, in which the development of well-calibrated, Fourier transform spectrometers in orbit is proposed, for monitoring these changes in the Earth's OLR spectrum.

  7. Photoinduced diffusion molecular transport

    NASA Astrophysics Data System (ADS)

    Rozenbaum, Viktor M.; Dekhtyar, Marina L.; Lin, Sheng Hsien; Trakhtenberg, Leonid I.

    2016-08-01

    We consider a Brownian photomotor, namely, the directed motion of a nanoparticle in an asymmetric periodic potential under the action of periodic rectangular resonant laser pulses which cause charge redistribution in the particle. Based on the kinetics for the photoinduced electron redistribution between two or three energy levels of the particle, the time dependence of its potential energy is derived and the average directed velocity is calculated in the high-temperature approximation (when the spatial amplitude of potential energy fluctuations is small relative to the thermal energy). The thus developed theory of photoinduced molecular transport appears applicable not only to conventional dichotomous Brownian motors (with only two possible potential profiles) but also to a much wider variety of molecular nanomachines. The distinction between the realistic time dependence of the potential energy and that for a dichotomous process (a step function) is represented in terms of relaxation times (they can differ on the time intervals of the dichotomous process). As shown, a Brownian photomotor has the maximum average directed velocity at (i) large laser pulse intensities (resulting in short relaxation times on laser-on intervals) and (ii) excited state lifetimes long enough to permit efficient photoexcitation but still much shorter than laser-off intervals. A Brownian photomotor with optimized parameters is exemplified by a cylindrically shaped semiconductor nanocluster which moves directly along a polar substrate due to periodically photoinduced dipole moment (caused by the repetitive excited electron transitions to a non-resonant level of the nanocylinder surface impurity).

  8. Auditory Evoked Fields Elicited by Spectral, Temporal, and Spectral–Temporal Changes in Human Cerebral Cortex

    PubMed Central

    Okamoto, Hidehiko; Teismann, Henning; Kakigi, Ryusuke; Pantev, Christo

    2012-01-01

    Natural sounds contain complex spectral components, which are temporally modulated as time-varying signals. Recent studies have suggested that the auditory system encodes spectral and temporal sound information differently. However, it remains unresolved how the human brain processes sounds containing both spectral and temporal changes. In the present study, we investigated human auditory evoked responses elicited by spectral, temporal, and spectral–temporal sound changes by means of magnetoencephalography. The auditory evoked responses elicited by the spectral–temporal change were very similar to those elicited by the spectral change, but those elicited by the temporal change were delayed by 30–50 ms and differed from the others in morphology. The results suggest that human brain responses corresponding to spectral sound changes precede those corresponding to temporal sound changes, even when the spectral and temporal changes occur simultaneously. PMID:22593751

  9. Photoinduced electro-optics measurements of biosilica transformation to cristobalite

    SciTech Connect

    Fuchs, Ido; Aluma, Yaniv; Ilan, Micha; Kityk, Iwan; Mastai, Yitzhak

    2015-03-15

    In this paper we studied the photoinduced electro optics effects in the thermal transformation process of biosilica to cristobalite, at a relatively low temperature and ambient pressure. This process was characterized by a variety of standards techniques with emphasis on linear electro optic effect measurements. Overall we demonstrated that photoinduced electro optics measurements are very sensitive to the transformation from amorphous structure of silica in the natural sponge samples to laminar string morphology of cristobalite. With this technique we could probe the change in the samples chirality from achiral bio silica to chiral cristobalite structure. Furthermore it is shown that natural biosilica have photoinduced linear electro optics respond indicating the chiral natural of biosilica. - Graphical abstract: The phase transformation of biosilica from marine sponges to Cristobalite under thermal treatment was investigated using photoinduced electro optics measurements. The figure shows the changes of the electro-optic coefficient of cristobalite and biosilica. - Highlights: • We examine phase transformation of biosilica. • We report transition from amorphous biosilica to crystalline Cristobalite. • Biosilica transformation to Cristobalite at temperature of 850 °C. • Biosilica transformation is studied with photoinduced measurements. • We examine changes in the photoinduced linear electro optics properties.

  10. Photoinduced mass transport in azo compounds

    NASA Astrophysics Data System (ADS)

    Klismeta, K.; Teteris, J.; Aleksejeva, J.

    2013-12-01

    The photoinduced changes of optical properties in azobenzene containing compound thin films were studied under influence of polarized and non-polarized 532 nm laser light. Under influence of light azo compounds experience trans-cis isomerisation process, that can be observed in the absorbance spectrum of the sample. If the light is linearly polarized, molecules align perpendicularly to the electric field vector and as a result photoinduced dichroism and birefringence is obtained. If a known lateral polarization modulation of the light beam is present, mass transport of the azobenzene containing compound occurs. By measuring the surface relief with a profilometer the direction of mass transport can be determined. The studies of this work show that direct holographic recording of surface relief gratings can be used in optoelectronics, telecommunications and data storage.

  11. Spectral changes in the zenith skylight during total solar eclipses.

    PubMed

    Hall, W N

    1971-06-01

    The relative spectral intensity of the zenith sky was measured with an optical scanning spectrometer at Nantucket Island, Massachusetts, during the total solar eclipse of 7 March 1970. The spectral ratios I(5100 A)/I(4300 A) and I(5900 A)/I(5100 A) at Nantucket remained unchanged for 96% or less obscuration of the sun by the moon. The results are compared with other recent relative spectral intensity measurements made during total solar eclipses. Comparison with other eclipse measurements for solar elevation angle at totality less than 45 degrees shows a blue color shift consistent with rayleigh scattering. Eclipses with solar elevation angles at totality greater than 45 degrees do not show consistent color shifts. This inconsistency may be due to difficulty in establishing a suitable reference spectrum for comparison with the spectral distribution of the zenith sky at totality. Selection of a suitable reference spectrum is discussed.

  12. Quantum pattern formation dynamics of photoinduced nucleation

    NASA Astrophysics Data System (ADS)

    Ishida, Kunio; Nasu, Keiichiro

    2008-06-01

    We study the dynamics of quantum pattern formation processes in molecular crystals which is concomitant with photoinduced nucleation. Since the nucleation process in coherent regime is driven by the nonadiabatic transition in each molecule followed by the propagation of phonons, it is necessary to take into account the quantum nature of both electrons and phonons in order to pursue the dynamics of the system. Therefore, we employ a model of localized electrons coupled with a quantized phonon mode and solve the time-dependent Schrödinger equation numerically. We found that there is a minimal size of clusters of excited molecules which triggers the photoinduced nucleation process; i.e., nucleation does not take place unless sufficient photoexcitation energy is concentrated within a narrow area of the system. We show that this result means that the spatial distribution of photoexcited molecules plays an important role in the nonlinearity of the dynamics and also in the optical properties observed in experiments. We calculate the conversion ratio, the rate of cluster formation, and correlation functions to reveal the dynamical properties of the pattern formation process; the initial dynamics of the photoinduced structural change is discussed from the viewpoint of pattern formation.

  13. Effect of irradiance spectra on the photoinduced toxicity of three polycyclic aromatic hydrocarbons

    SciTech Connect

    Diamond, S.A.; Mount, D.R.; Burkhard, L.P.; Ankley, G.T.; Makynen, E.A.; Leonard, E.N.

    2000-05-01

    Photoinduced toxicity of polycyclic aromatic hydrocarbons (PAHs) is dependent on the concentration of compounds present and the dose of light received. Of the light present, only those wavelengths absorbed by the compound have the potential to initiate the photochemical events underlying phototoxicity. This suggests that variation in light spectra present in natural waters, arising from variation in dissolved organic carbon composition, is an important determinant of phototoxicity risk in specific, PAH-contaminated waterbodies. To quantify the effect of environmentally realistic variation in light spectra on toxicity, brine shrimp (Artemia salina) assays were conducted under various light spectra and with three PAHs (pyrene, fluoranthene, and anthracene) of known phototoxicity potential. In these spectral assays, the total ultraviolet light present was equivalent; only the spectral characteristics varied. Based on the absorbance spectra of these PAHs, it was predicted that toxicity, quantified using immobilization as the endpoint, would vary significantly among light spectra in pyrene assays, but not in anthracene assays, and that variation in toxicity in fluoranthene assays would be intermediate. The results supported these assumptions. In the pyrene exposures, the glass filter time to 50% population immobilization (IT50) (39.5 min) was 117% longer than the KCr filter IT50 (18.2 min). In the fluoranthene exposures, the glass filter IT50 (49.5 min) was 27% longer than the KCr filter IT50 (39.1 min). In the anthracene exposures, the glass filter IT50 (62.2 min) was not statistically different from the KCr filter IT50 (63.8 min). Comparison of these results with the results of assays conducted under neutral-density filters (that change intensity but not spectral distribution) demonstrate that multiplying spectral intensity by wavelength-specific absorbance accurately predicts relative photoinduced toxicity among the experimental treatments. These results indicate

  14. Changes in spectral sensitivity of multiplier phototubes resulting from changes in temperature.

    PubMed

    Boileau, A R; Miller, F D

    1967-07-01

    The change in cathode spectral sensitivity of Westinghouse WX 4582 (S-11) and RCA 1P21(S-4) multiplier phototubes was measured across the visible spectrum, i.e., from 400 nm to 700 nm, for various temperature changes, both increases and decreases. Two methods were used for these measurements, viz., an adaptation of the Hardy spectrophotometer and the use of an environmental chamber. A decrease in temperature usually caused an increase in sensitivity in the short wavelength part of the spectrum and a decrease (as much as 90% at 700 nm) in the long wavelength part of the spectrum, with the crossover point (no appreciable change of sensitivity with change of temperature) at about 590 nm. An increase in temperature was accompanied by a reversal of spectral sensitivity changes, i.e., a decrease in the short wavelength part of spectrum and an increase in the long wavelength part of the spectrum. The change in cathode sensitivity varied with different types of phototubes and with phototubes of the same type.

  15. Intra-QRS Spectral Changes Accompany ST Segment Changes During Episodes of Myocardial Ischemia

    PubMed Central

    Gramatikov, Boris; Iyer, Vivek

    2014-01-01

    Background Coronary artery disease and myocardial ischemia cause substantial morbidity and mortality. While ischemia is traditionally diagnosed on the 12-lead electrocardiogram (ECG) by shifts in the ST segment, electrical changes are also produced within the QRS complex during depolarization of ischemic ventricular tissue, though these are often of small amplitude and can be missed in traditional ECG analysis. We explore the utility of an easily implemented spectral analysis method for detecting intra-QRS changes during episodes of myocardial ischemia, using Holter recordings from the European ST-T database. Methods Time-frequency distributions of QRS complexes from each recording were computed using the continuous wavelet transform. Indices corresponding to frequency content of four overlapping frequency bands were computed: F1 (24–35 Hz), F2 (30–45 Hz), F3 (40–60 Hz), and F4 (50–80 Hz). Values of these indices were compared during annotated episodes of ST change and during a baseline during the recording. Results Marked changes in intra-QRS frequency content were identified during ischemia, grouped by ECG lead analyzed. In lead III, a pronounced and statistically significant increase in the highest frequency sub-bands (F3 and F4) was consistently observed. Analysis of anterior precordial leads also showed significant increases in F4. Conclusions Intra-QRS time-frequency analysis using the continuous wavelet transform can identify a spectral signature corresponding to myocardial ischemia in the range 24–80 Hz. Intra-QRS spectral analysis has the potential for many clinical applications. PMID:25266140

  16. Fluoride anion sensing mechanism of 2-ureido-4[1H]-pyrimidinone quadruple hydrogen-bonded supramolecular assembly: photoinduced electron transfer and partial configuration change.

    PubMed

    Chen, Jun-Sheng; Zhou, Pan-Wang; Li, Guang-Yue; Chu, Tian-Shu; He, Guo-Zhong

    2013-05-02

    The fluoride anion sensing mechanism of 6-methyl-5-(9-methylene-anthracene)-(2-butylureido-4[1H]-pyrimidinone) (AnUP) has been investigated using the DFT/TDDFT method. The theoretical results indicate that the proton of the N3-H3 group in pyrimidine moiety is captured by the added fluoride anion and then deprotonated. The calculated vertical excitation energies of AnUP-dimer and its deprotonated form agree well with the experimental results. The molecular orbital analysis demonstrates that the first excited state (S1) of AnUP-dimer is a local excited state with a π-π* transition, whereas for the deprotonated form, S1 is a completely charge-separation state and is responsible for the photoinduced electron transfer (PET) process. The PET process from anthracene to the pyrimidine moiety leads to the fluorescence quenching.

  17. Photoinduced electro-optics measurements of biosilica transformation to cristobalite

    NASA Astrophysics Data System (ADS)

    Fuchs, Ido; Aluma, Yaniv; Ilan, Micha; Kityk, Iwan; Mastai, Yitzhak

    2015-03-01

    In this paper we studied the photoinduced electro optics effects in the thermal transformation process of biosilica to cristobalite, at a relatively low temperature and ambient pressure. This process was characterized by a variety of standards techniques with emphasis on linear electro optic effect measurements. Overall we demonstrated that photoinduced electro optics measurements are very sensitive to the transformation from amorphous structure of silica in the natural sponge samples to laminar string morphology of cristobalite. With this technique we could probe the change in the samples chirality from achiral bio silica to chiral cristobalite structure. Furthermore it is shown that natural biosilica have photoinduced linear electro optics respond indicating the chiral natural of biosilica.

  18. Optimal spectral tracking--adapting to dynamic regime change.

    PubMed

    Brittain, John-Stuart; Halliday, David M

    2011-01-30

    Real world data do not always obey the statistical restraints imposed upon them by sophisticated analysis techniques. In spectral analysis for instance, an ergodic process--the interchangeability of temporal for spatial averaging--is assumed for a repeat-trial design. Many evolutionary scenarios, such as learning and motor consolidation, do not conform to such linear behaviour and should be approached from a more flexible perspective. To this end we previously introduced the method of optimal spectral tracking (OST) in the study of trial-varying parameters. In this extension to our work we modify the OST routines to provide an adaptive implementation capable of reacting to dynamic transitions in the underlying system state. In so doing, we generalise our approach to characterise both slow-varying and rapid fluctuations in time-series, simultaneously providing a metric of system stability. The approach is first applied to a surrogate dataset and compared to both our original non-adaptive solution and spectrogram approaches. The adaptive OST is seen to display fast convergence and desirable statistical properties. All three approaches are then applied to a neurophysiological recording obtained during a study on anaesthetic monitoring. Local field potentials acquired from the posterior hypothalamic region of a deep brain stimulation patient undergoing anaesthesia were analysed. The characterisation of features such as response delay, time-to-peak and modulation brevity are considered.

  19. Spectral mode changes in an alkali rf discharge

    SciTech Connect

    Camparo, J. C.; Mackay, R.

    2007-03-01

    As a result of observations made by Shaw (M.S. thesis, Cornell University, 1964) in the mid-1960s, alkali rf discharges are known to operate in two spectral modes, the so-called ring mode and the red mode. Experience has shown that the ring mode is best for discharge lamps used in quantum-electronic devices such as atomic clocks and optically pumped magnetometers and that the performance of these devices seriously degrades when the lamp operates in the red mode. Understanding the origin of these modes therefore has application to understanding and improving various quantum-electronic devices. Here we show that Shaw's model for these modes is inconsistent with observation, and we propose an alternate model based on the role of radiation trapping in multistep ionization.

  20. Spectral and temporal resolutions of information-bearing acoustic changes for understanding vocoded sentencesa)

    PubMed Central

    Stilp, Christian E.; Goupell, Matthew J.

    2015-01-01

    Short-time spectral changes in the speech signal are important for understanding noise-vocoded sentences. These information-bearing acoustic changes, measured using cochlea-scaled entropy in cochlear implant simulations [CSECI; Stilp et al. (2013). J. Acoust. Soc. Am. 133(2), EL136–EL141; Stilp (2014). J. Acoust. Soc. Am. 135(3), 1518–1529], may offer better understanding of speech perception by cochlear implant (CI) users. However, perceptual importance of CSECI for normal-hearing listeners was tested at only one spectral resolution and one temporal resolution, limiting generalizability of results to CI users. Here, experiments investigated the importance of these informational changes for understanding noise-vocoded sentences at different spectral resolutions (4–24 spectral channels; Experiment 1), temporal resolutions (4–64 Hz cutoff for low-pass filters that extracted amplitude envelopes; Experiment 2), or when both parameters varied (6–12 channels, 8–32 Hz; Experiment 3). Sentence intelligibility was reduced more by replacing high-CSECI intervals with noise than replacing low-CSECI intervals, but only when sentences had sufficient spectral and/or temporal resolution. High-CSECI intervals were more important for speech understanding as spectral resolution worsened and temporal resolution improved. Trade-offs between CSECI and intermediate spectral and temporal resolutions were minimal. These results suggest that signal processing strategies that emphasize information-bearing acoustic changes in speech may improve speech perception for CI users. PMID:25698018

  1. An empirical link between the spectral colour of climate and the spectral colour of field populations in the context of climate change.

    PubMed

    García-Carreras, Bernardo; Reuman, Daniel C

    2011-09-01

    1. The spectral colour of population dynamics and its causes have attracted much interest. The spectral colour of a time series can be determined from its power spectrum, which shows what proportion of the total variance in the time series occurs at each frequency. A time series with a red spectrum (a negative spectral exponent) is dominated by low-frequency oscillations, and a time series with a blue spectrum (a positive spectral exponent) is dominated by high-frequency oscillations. 2. Both climate variables and population time series are characterised by red spectra, suggesting that a population's environment might be partly responsible for its spectral colour. Laboratory experiments and models have been used to investigate this potential link. However, no study using field data has directly tested whether populations in redder environments are redder. 3. This study uses the Global Population Dynamics Database together with climate data to test for this effect. We found that the spectral exponent of mean summer temperatures correlates positively and significantly with population spectral exponent. 4. We also found that over the last century, temperature climate variables on most continents have become bluer. 5. Although population time series are not long or abundant enough to judge directly whether their spectral colours are changing, our two results taken together suggest that population spectral colour may be affected by the changing spectral colour of climate variables. Population spectral colour has been linked to extinction; we discuss the potential implications of our results for extinction probability.

  2. [The changes of forest canopy spectral reflectance with seasons in Xiaoxing'anling].

    PubMed

    Xu, Guang-Cai; Pang, Yong; Li, Zeng-Yuan; Zhao, Kai-Rui; Liu, Lu-Xia

    2013-12-01

    The ASD FieldSpec portable spectrometer was adopted to collect canopy reflectance spectrum data of the 9 main tree species in study area by a long-term observation to get the data of the four seasons Then the smoothed reflectance curve and the first derivation curve from 350 to 1400 nm and several commonly used vegetation spectral characteristic parameters were generated to analyse seasonal change characteristics and variation of the 9 tree species in visible and near-infrared band and to explore the best band characteristics and period for species identification. The results showed that different trees had different and rather unique spectral features during the four seasons. The spectral characteristics of the deciduous trees have regular changes with the cycle of the seasons, whereas those of the evergreen tree species have no significant changes in one year. As well changes in the spectral characteristics could effectively reflect forest phenology changes, and it is proposed that the optimal strategy for tree species classification may be the integration and analysis of multi-seasonal spectral data. Evergreen trees and deciduous trees in the winter have obvious differences in the canopy spectral characteristics and the best single-season remote sensing data for tree species recognition is in summer.

  3. Photoinduced surface reactions on TiO{sub 2} and SrTiO{sub 3} films: Photocatalytic oxidation and photoinduced hydrophilicity

    SciTech Connect

    Miyauchi, Masahiro; Nakajima, Akira; Fujishima, Akira; Hashimoto, Kazuhito; Watanabe, Toshiya

    2000-01-01

    In the present study, the authors have evaluated photocatalytic activities and photoinduced wettabilities for TiO{sub 2} and SrTiO{sub 3} films. Although both types of films had almost the same photocatalytic oxidation activity, photoinduced wettabilities of these films showed different phenomena. The photoinduced hydrophilicity peculiar to TiO{sub 2} is not caused by the photocatalytic oxidation of organic compounds adsorbed on the surface. The highly hydrophilic surface of TiO{sub 2} is ascribed to photogenerated Ti{sup 3+} defect sites that are favorable for dissociative water absorption. The yield of this photoinduced hydrophilic reaction is not clear at the present time. It is noted that this reaction involves a surface structural change, which should not require a high quantum efficiency as compared to conventional photocatalytic oxidation.

  4. Kinetics of photoinduced anisotropy in bacteriorhodopsin film under two pumping beams.

    PubMed

    Han, Junhe; Yao, Baoli; Gao, Peng; Chen, Liju; Wang, Yingli; Lei, Ming

    2008-07-20

    Photoinduced anisotropy in bacteriorhodopsin (BR) film arises from the selective bleaching of BR molecules to linearly polarized light. The kinetics of photoinduced anisotropy excited by single and two pumping beams are investigated theoretically and experimentally. Compared with a single pumping beam (650 nm), which produces comparatively small photoinduced anisotropy, dual-wavelength linearly polarized pumping beams (650 and 405 nm) can obviously change the photoinduced anisotropy. When the polarization orientation of the 405 nm pumping beam is perpendicular to that of the 650 nm pumping beam, the peak and steady values of the photoinduced anisotropy kinetic curves are remarkably enhanced. But when the two pumping beams have parallel polarization orientation, the peak and steady values are restrained. At a fixed intensity of the 650 nm pumping beam, there exists an optimal intensity for the 405 nm pumping beam to maximize the value of the photoinduced anisotropy. The photoinduced transmittance of the polarizer-BR-analyzer system is modulated by the polarization angle of the 405 nm pumping beam in an approximate-cosine form.

  5. Photoinduced Fusion of Lipid Bilayer Membranes.

    PubMed

    Suzuki, Yui; Nagai, Ken H; Zinchenko, Anatoly; Hamada, Tsutomu

    2017-03-14

    We have developed a novel system for photocontrol of the fusion of lipid vesicles through the use of a photosensitive surfactant containing an azobenzene moiety (AzoTAB). Real-time microscopic observations clarified a change in both the surface area and internal volume of vesicles during fusion. We also determined the optimal cholesterol concentrations and temperature for inducing fusion. The mechanism of fusion can be attributed to a change in membrane tension, which is caused by the solubilization of lipids through the isomerization of AzoTAB. We used a micropipet technique to estimate membrane tension and discuss the mechanism of fusion in terms of membrane elastic energy. The obtained results regarding this novel photoinduced fusion could lead to a better understanding of the mechanism of membrane fusion in living cells and may also see wider applications, such as in drug delivery and biomimetic material design.

  6. Maturational changes in automated EEG spectral power analysis in preterm infants.

    PubMed

    Niemarkt, Hendrik J; Jennekens, Ward; Pasman, Jaco W; Katgert, Titia; Van Pul, Carola; Gavilanes, Antonio W D; Kramer, Boris W; Zimmermann, Luc J; Bambang Oetomo, Sidarto; Andriessen, Peter

    2011-11-01

    Our study aimed at automated power spectral analysis of the EEG in preterm infants to identify changes of spectral measures with maturation. Weekly (10-20 montage) 4-h EEG recordings were performed in 18 preterm infants with GA <32 wk and normal neurological follow-up at 2 y, resulting in 79 recordings studied from 27(+4) to 36(+3) wk of postmenstrual age (PMA, GA + postnatal age). Automated spectral analysis was performed on 4-h EEG recordings. The frequency spectrum was divided in delta 1 (0.5-1 Hz), delta 2 (1-4 Hz), theta (4-8 Hz), alpha (8-13 Hz), and beta (13-30 Hz) band. Absolute and relative power of each frequency band and spectral edge frequency were calculated. Maturational changes in spectral measures were observed most clearly in the centrotemporal channels. With advancing PMA, absolute powers of delta 1 to 2 and theta decreased. With advancing PMA, relative power of delta 1 decreased and relative powers of alpha and beta increased, respectively. In conclusion, with maturation, spectral analysis of the EEG showed a significant shift from the lower to the higher frequencies. Computer analysis of EEG will allow an objective and reproducible analysis for long-term prognosis and/or stratification of clinical treatment.

  7. The contribution of durational and spectral changes to the Lombard speech intelligibility benefit.

    PubMed

    Cooke, Martin; Mayo, Catherine; Villegas, Julián

    2014-02-01

    Speech produced in the presence of noise (Lombard speech) is typically more intelligible than speech produced in quiet (plain speech) when presented at the same signal-to-noise ratio, but the factors responsible for the Lombard intelligibility benefit remain poorly understood. Previous studies have demonstrated a clear effect of spectral differences between the two speech styles and a lack of effect of fundamental frequency differences. The current study investigates a possible role for durational differences alongside spectral changes. Listeners identified keywords in sentences manipulated to possess either durational or spectral characteristics of plain or Lombard speech. Durational modifications were produced using linear or nonlinear time warping, while spectral changes were applied at the global utterance level or to individual time frames. Modifications were made to both plain and Lombard speech. No beneficial effects of durational increases were observed in any condition. Lombard sentences spoken at a speech rate substantially slower than their plain counterparts also failed to reveal a durational benefit. Spectral changes to plain speech resulted in large intelligibility gains, although not to the level of Lombard speech. These outcomes suggest that the durational increases seen in Lombard speech have little or no role in the Lombard intelligibility benefit.

  8. Using Spectral Methods to Quantify Changes in Temperature Variability across Frequencies

    NASA Astrophysics Data System (ADS)

    Sun, S.; McInerney, D.; Stein, M.; Leeds, W.; Poppick, A. N.; Nazarenko, L.; Schmidt, G. A.; Moyer, E. J.

    2014-12-01

    Changes in future surface temperature variability are of great scientific and societal interest. Since the impact of variability on human society depends on not only the magnitude but also the frequency of variations, shifts in the marginal distribution of temperatures do not provide enough information for impacts assessment. Leeds et al (2014) proposed a method to quantify changes in variability of temperature at distinct temporal frequencies by estimating the ratio of the spectral densities of temperature between pre-industrial and equilibrated future climates. This spectral ratio functions well as a metric to quantify temperature variability shifts in climate model output. In this study, we apply the method of Leeds et al (2014) to explore the temperature variability changes under increased radiative forcing. We compare changes in variability in higher-CO2 climates across two different climate models (CCSM3 from the National Center for Atmospheric Research and GISS-E2-R from NASA Goddard Institute for Space Studies), and changes driven by two different forcing agents (CO2 and solar radiation) within the same model (CCSM3). In all cases we use only the equilibrium stages of model runs extended several thousand years after an abrupt forcing change is imposed. We find a number of results. First, changes in temperature variability differ by frequency in most regions, confirming the need for spectral methods. Second, changes are similar regardless of forcing agents. In experiments with abruptly increased CO2 and solar forcing designed to produce the same change in global mean temperature, the distributions and magnitudes of spectral ratio changes are nearly identical. Finally, projections of variability changes differ across models. In CCSM3, temperature variability decreases in most regions and at most frequencies. Conversely, in GISS-E2-R, temperature variability tends to increase over land. The discrepancy between CCSM3 and the GISS-E-R highlights the need for

  9. Photo-induced Defects in Semiconductors

    NASA Astrophysics Data System (ADS)

    Redfield, David; Bube, Richard H.

    2006-03-01

    1. Introduction: metastable defects; 2. III-V compounds: DX2 and EL2 centers; 3. Other crystalline materials; 4. Hydrogenated amorphous silicon: properties of defects; 5. Hydrogenated amorphous silicon: photo-induced defect kinetics and processes; 6. Other amorphous semiconductors; 7. Photo-induced defect effects in devices; References; Index.

  10. Characterizing microstructural changes of skeletal muscle tissues using spectral transformed Mueller matrix polarization parameters

    NASA Astrophysics Data System (ADS)

    He, Chao; He, Honghui; Chang, Jintao; Ma, Hui

    2016-03-01

    Polarization imaging techniques are recognized as potentially powerful tools to detect the structural changes of biological tissues. Meanwhile, spectral features of the scattered light can also provide abundant microstructural information, therefore can be applied in biomedical studies. In this paper, we adopt the polarization reflectance spectral imaging to analyze the microstructural changes of hydrolyzing skeletal muscle tissues. We measure the Mueller matrix, which is a comprehensive description of the polarization properties, of the bovine skeletal muscle samples in different periods of time, and analyze its behavior using the multispectral Mueller matrix transformation (MMT) technique. The experimental results show that for bovine skeletal muscle tissues, the backscattered spectral MMT parameters have different values and variation features at different stages. We can also find the experimental results indicate that the stages of hydrolysis for bovine skeletal muscle samples can be judged by the spectral MMT parameters. The results presented in this work show that combining with the spectral technique, the MMT parameters have the potential to be used as tools for meat quality detection and monitoring.

  11. Tracking Voice Change after Thyroidectomy: Application of Spectral/Cepstral Analyses

    ERIC Educational Resources Information Center

    Awan, Shaheen N.; Helou, Leah B.; Stojadinovic, Alexander; Solomon, Nancy Pearl

    2011-01-01

    This study evaluates the utility of perioperative spectral and cepstral acoustic analyses to monitor voice change after thyroidectomy. Perceptual and acoustic analyses were conducted on speech samples (sustained vowel /[alpha]/ and CAPE-V sentences) provided by 70 participants (36 women and 34 men) at four study time points: prior to thyroid…

  12. Photo-induced and electrooptic properties of (Pb,La)(Zr,Ti) O{sub 3} films for optical memories

    SciTech Connect

    Dimos, D.; Potter, B.G.; Sinclair, M.B.; Tuttle, B.A.; Warren, W.L.

    1993-09-01

    Photo-induced hysteresis changes and electrooptic effects in sol-gel Pb(Zr,Ti)0{sub 3} (PZT) and PLZT films have been studied in an effort to evaluate these materials for optical memory applications. The films exhibit two types of photo-induced changes in their hysteresis behavior which are suitable for optical storage. Both types of photo-induced hysteresis changes are due to trapping of photo-generated charge carriers at sites which minimize internal depolarizing fields. The photo-induced changes are reproducible and stable, which indicates that the charge traps are stable. However, improvements in photosensitivity will be required to develop a competitive technology for optical memories. In addition, polarization-dependent changes in the refractive indices can be the basis of a nondestructive optical readout technique. The index changes of films have been determined using a waveguide refractometry technique, which allows the extraordinary and ordinary index changes to be obtained independently.

  13. Photo-induced and electrooptic properties of (Pb,La)(Zr,Ti)O3 films for optical memories

    NASA Astrophysics Data System (ADS)

    Dimos, D.; Potter, B. G.; Sinclair, M. B.; Tuttle, B. A.; Warren, W. L.

    Photo-induced hysteresis changes and electro-optic effects in sol-gel Pb(Zr,Ti)03 (PZT) and PLZT films have been studied in an effort to evaluate these materials for optical memory applications. The films exhibit two types of photo-induced changes in their hysteresis behavior which are suitable for optical storage. Both types of photo-induced hysteresis changes are due to trapping of photo-generated charge carriers at sites which minimize internal depolarizing fields. The photo-induced changes are reproducible and stable, which indicates that the charge traps are stable. However, improvements in photosensitivity will be required to develop a competitive technology for optical memories. In addition, polarization-dependent changes in the refractive indices can be the basis of a nondestructive optical readout technique. The index changes of films have been determined using a waveguide refractometry technique, which allows the extraordinary and ordinary index changes to be obtained independently.

  14. Modeling photoinduced fluorescence enhancement in semiconductor nanocrystal arrays

    NASA Astrophysics Data System (ADS)

    Maenosono, Shinya

    2003-07-01

    Photoinduced fluorescence enhancement (PFE) in semiconductor nanocrystal (NC) arrays is modeled based on the rate equations for ground-state, excited-state and photoionized NCs in the array. The photoionization process is broken down into fast and slow ionization processes, which are expected to relate to blinking and darkening phenomena, respectively. Consequently, PFE behavior is found to change drastically, as it depends on both the intrinsic properties of NCs, and on external conditions, such as surface-capping molecules and atmosphere.

  15. Spectral Index Changes with Brightness for γ-Ray Loud Blazars

    NASA Astrophysics Data System (ADS)

    Yang, J. H.; Yang, R. S.; Nie, J. J.; Fan, J. H.

    2014-09-01

    Based on Fermi 1FGL and 2FGL data, a sample of 572 γ-ray loud blazars are selected, in which each sources has both γ-ray flux and spectral index in 1FGL and 2FGL, respectively. Theoretic relation of spectral index changes depending on γ-ray brightness is obtained. The correlations between the ratio of γ-ray flux densities and the differences of the γ-ray spectral indices are discussed for the three subclasses of HBL, LBL and FSRQs. Results show that the ratio is related with the differences for the three subclasses. It is consistent with the theoretical result and it indicates that the spectrum becomes flat as the source brightens in the γ-ray band.

  16. RAPID SPECTRAL CHANGES OF CYGNUS X-1 IN THE LOW/HARD STATE WITH SUZAKU

    SciTech Connect

    Yamada, S.; Makishima, K.; Negoro, H.; Torii, S.; Noda, H.; Mineshige, S.

    2013-04-20

    Rapid spectral changes in the hard X-ray on a timescale down to {approx}0.1 s are studied by applying a ''shot analysis'' technique to the Suzaku observations of the black hole binary Cygnus X-1, performed on 2008 April 18 during the low/hard state. We successfully obtained the shot profiles, covering 10-200 keV with the Suzaku HXD-PIN and HXD-GSO detector. It is notable that the 100-200 keV shot profile is acquired for the first time owing to the HXD-GSO detector. The intensity changes in a time-symmetric way, though the hardness changes in a time-asymmetric way. When the shot-phase-resolved spectra are quantified with the Compton model, the Compton y-parameter and the electron temperature are found to decrease gradually through the rising phase of the shot, while the optical depth appears to increase. All the parameters return to their time-averaged values immediately within 0.1 s past the shot peak. We have not only confirmed this feature previously found in energies below {approx}60 keV, but also found that the spectral change is more prominent in energies above {approx}100 keV, implying the existence of some instant mechanism for direct entropy production. We discuss possible interpretations of the rapid spectral changes in the hard X-ray band.

  17. Detecting changes in surface moisture and water table position with spectral changes in surface vegetation in northern peatlands

    NASA Astrophysics Data System (ADS)

    Meingast, Karl M.

    Due to warmer and drier conditions, wildland fire has been increasing in extent into peatland ecosystems during recent decades. As such, there is an increasing need for broadly applicable tools to detect surface peat moisture, in order to ascertain the susceptibility of peat burning, and the vulnerability of deep peat consumption in the event of a wildfire. In this thesis, a field portable spectroradiometer was used to measure surface reflectance of two Sphagnum moss dominated peatlands. Relationships were developed correlating spectral indices to surface moisture as well as water table position. Spectral convolutions were also applied to the high resolution spectra to represent spectral sensitivity of earth observing sensors. Band ratios previously used to monitor surface moisture with these sensors were assessed. Strong relationships to surface moisture and water table position are evident for both the narrowband indices as well as broadened indices. This study also found a dependence of certain spectral relationships on changes in vegetation cover by leveraging an experimental vegetation manipulation. Results indicate broadened indices employing the 1450-1650 nm region may be less stable under changing vegetation cover than those located in the 1200 nm region.

  18. Photoinduced translational molecular mobility in solid nanostructured azo dye films

    SciTech Connect

    Ezhov, A A; Kozenkov, V M; Magnitskii, Sergey A; Nagorskii, Nikolay M; Panov, Vladimir I

    2011-11-30

    A new mechanism controlling the molecular motion in thin azo-containing films during a photoinduced change in the surface nanorelief is found. It is shown experimentally that exposure of a solid AD-1 azo dye, deposited on a glass substrate, to incoherent linearly polarised light leads to formation of nanostructures with a characteristic size of 200 nm, which are similar to droplets of melt of this dye on the same substrate. It is shown that photoinduced mass transport in a solid AD-1 azo dye film can be explained by the mobility of molecules related to their trans-cis-photoisomerisation, which leads to film softening with subsequent formation of spherical protrusions under surface tension forces.

  19. Senegalese land surface change analysis and biophysical parameter estimation using NOAA AVHRR spectral data

    NASA Technical Reports Server (NTRS)

    Vukovich, Fred M.; Toll, David L.; Kennard, Ruth L.

    1989-01-01

    Surface biophysical estimates were derived from analysis of NOAA Advanced Very High Spectral Resolution (AVHRR) spectral data of the Senegalese area of west Africa. The parameters derived were of solar albedo, spectral visible and near-infrared band reflectance, spectral vegetative index, and ground temperature. Wet and dry linked AVHRR scenes from 1981 through 1985 in Senegal were analyzed for a semi-wet southerly site near Tambacounda and a predominantly dry northerly site near Podor. Related problems were studied to convert satellite derived radiance to biophysical estimates of the land surface. Problems studied were associated with sensor miscalibration, atmospheric and aerosol spatial variability, surface anisotropy of reflected radiation, narrow satellite band reflectance to broad solar band conversion, and ground emissivity correction. The middle-infrared reflectance was approximated with a visible AVHRR reflectance for improving solar albedo estimates. In addition, the spectral composition of solar irradiance (direct and diffuse radiation) between major spectral regions (i.e., ultraviolet, visible, near-infrared, and middle-infrared) was found to be insensitive to changes in the clear sky atmospheric optical depth in the narrow band to solar band conversion procedure. Solar albedo derived estimates for both sites were not found to change markedly with significant antecedent precipitation events or correspondingly from increases in green leaf vegetation density. The bright soil/substrate contributed to a high albedo for the dry related scenes, whereas the high internal leaf reflectance in green vegetation canopies in the near-infrared contributed to high solar albedo for the wet related scenes. The relationship between solar albedo and ground temperature was poor, indicating the solar albedo has little control of the ground temperature. The normalized difference vegetation index (NDVI) and the derived visible reflectance were more sensitive to antecedent

  20. Mineralogical, Spectral, and Compositional Changes During Heating of Hydrous Carbonaceous Chondrites

    NASA Technical Reports Server (NTRS)

    Nakamura, T.; Matsuoka, M.; Yamashita, S.; Sato, Y.; Mogi, K.; Enokido, Y.; Nakata, A.; Okumura, S.; Furukawa, Y.; Zolensky, M.

    2017-01-01

    Hydrous carbonaceous chondrites experienced hydration and subsequent dehydration by heating, which resulted in a variety of mineralogical and spectral features [e. g., 1-6]. The degree of heating is classified according to heating stage (HS) II to IV based on mineralogy of phyllosilicates [2], because they change, with elevating temperature, to poorly crystal-line phases and subsequently to aggregates of small secondary anhydrous silicates of mainly olivine. Heating of hydrous carbonaceous chondrites also causes spectral changes and volatile loss [3-6]. Experimental heating of Murchison CM chondrite showed flattening of whole visible-near infrared spectra, especially weakening of the 3µm band strength [1, 4, 7]. In order to understand mineralogical, spectral, and compositional changes during heating of hydrous carbonaceous chondrites, we have carried out systematic investigation of mineralogy, reflectance spectra, and volatile composition of hydrated and dehydrated carbonaceous chondrites as well as experimentally-heated hydrous carbonaceous chondrites. In addition, we investigated reflectance spectra of tochilinite that is a major phase of CM chondrites and has a low dehydration temperature (250degC).

  1. Changes in EEG mean frequency and spectral purity during spontaneous alpha blocking.

    PubMed

    Goncharova, I I; Barlow, J S

    1990-09-01

    Spontaneously occurring brief periods of lower voltage irregular activity occurring amid a background of alpha activity (i.e., alpha blocking) in eyes-closed resting occipital EEG recordings from 32 healthy human subjects have been investigated to determine the extent of changes of mean frequency and of spectral purity (degree of regularity/irregularity of the EEG activity) during such periods. New methods for determining mean frequency and spectral purity (the latter as a new measure, the Spectral Purity Index, which has a maximum value of 1.0 for a pure sine wave) permit their conjoint evaluation over a 0.5 sec window that is advanced along the EEG in 0.1 sec steps, thus permitting almost continuous feature extraction. The findings indicate that, although spectral purity invariably decreased during the periods of lower voltage irregular activity, the mean frequency remained relatively unaltered, i.e., it remained unchanged or it increased or decreased slightly but at most by 2.5 Hz. These results suggest that, at least for the periods of lower voltage irregular activity occurring spontaneously amid an alpha background during eyes-closed occipital EEG recordings, it may be inaccurate (as some authors have already suggested) to use the term 'low-voltage fast (or beta) activity.'

  2. Dynamics of photo-induced changes in the elastic characteristics of lithium niobate crystals doped with Jahn-Teller Fe2+ ions

    NASA Astrophysics Data System (ADS)

    Golenishchev-Kutuzov, A. V.; Golenishchev-Kutuzov, V. A.; Kalimullin, R. I.; Semennikov, A. V.

    2017-02-01

    The effect of admixture Jahn-Teller Fe2+ ions on the elastic characteristics of lithium niobate was studied. The appearance of photostrains and a change in elastic moduli under the influence of laser radiation was established, thus enabling the creation of device elements with optically controlled elastic characteristics.

  3. Effect of enhancement of spectral changes on speech intelligibility and clarity preferences for the hearing impaired.

    PubMed

    Chen, Jing; Baer, Thomas; Moore, Brian C J

    2012-04-01

    Most information in speech is carried in spectral changes over time, rather than in static spectral shape per se. A form of signal processing aimed at enhancing spectral changes over time was developed and evaluated using hearing-impaired listeners. The signal processing was based on the overlap-add method, and the degree and type of enhancement could be manipulated via four parameters. Two experiments were conducted to assess speech intelligibility and clarity preferences. Three sets of parameter values (one corresponding to a control condition), two types of masker (steady speech-spectrum noise and two-talker speech) and two signal-to-masker ratios (SMRs) were used for each masker type. Generally, the effects of the processing were small, although intelligibility was improved by about 8 percentage points relative to the control condition for one set of parameter values using the steady noise masker at -6 dB SMR. The processed signals were not preferred over those for the control condition, except for the steady noise masker at -6 dB SMR. Further work is needed to determine whether tailoring the processing to the characteristics of the individual hearing-impaired listener is beneficial.

  4. Spectral Changes in Metal Halide and High-Pressure Sodium Lamps Equipped with Electronic Dimming

    NASA Technical Reports Server (NTRS)

    Bubenheim, David L.; Sargis, Raman; Wilson, David

    1995-01-01

    Electronic dimming of high-intensity discharge lamps offers control of Photosynthetic Photon Flux (PPF) but is often characterized as causing significant spectral changes. Growth chambers with 400-W Metal Halide (MH) and High-Pressure Sodium (HPS) lamps were equipped with a dimmer system using Silicon-Controlled Rectifiers (SCR) as high-speed switches. Phase control operation turned the line power off for some period of the alternating current cycle. At full power, the electrical input to HPS and MH lamps was 480 W (root mean squared) and could be decreased to 267 W and 428 W, respectively, before the arc was extinguished. Concomitant with this decrease in input power, PPF decreased by 60% in HPS and 50% in MH. The HPS lamp has characteristic spectral peaks at 589 and 595 nm. As power to the HPS lamps was decreased, the 589-nm peak remained constant while the 595-nm peak decreased, equaling the 589-nm peak at 345-W input, and 589-nm peak was almost absent at 270-W input. The MH lamp has a broader spectral output but also has a peak at 589 nm and another smaller peak at 545 nm. As input power approached 428 W, the 589-nm peak shifted to 570 nm. While the spectrum changed as input power was decreased in the MH and HPS lamps, the phytochrome equilibrium ratio (P(sub ft):P(sub tot)) remains unchanged for both lamp types.

  5. Spectral and Textural Changes Observed in Sulfate Soil Deposits at Gusev Crater, Mars

    NASA Astrophysics Data System (ADS)

    Rice, M. S.; Bell, J. F.; Wang, A.; Johnson, J. R.; Arvidson, R. E.

    2009-12-01

    The Mars Exploration Rover (MER) Spirit has discovered deposits of bright yellowish and whitish soils that have been confirmed by Spirit’s Alpha Particle X-Ray Spectrometer (APXS), Mössbauer spectrometer, and Miniature Thermal Emission Spectrometer (Mini-TES) instruments to contain ferric sulfates and/or opaline silica. These deposits have important implications for the history of water at Gusev Crater, as they have been interpreted by Squyres et al. (2008, Science, 316, 738) to have formed in a hydrothermal environment. Repeated Pancam 11 color visible to short-wave near-IR observations have been made at the Tyrone, Kit Carson and Ulysess soil exposures, and changes in Vis-NIR spectra and/or soil texture and morphology have been observed at all three sites. We have identified at least three possible explanations for the observed changes: 1) dust deposition; 2) aeolian sorting; and/or 3) a mineralogic change after exposure to martian surface conditions. To better characterize how and why these soils are changing with time, we present a detailed multispectral analysis of the seven Pancam image sequences at Tyrone, the two at Kit Carson, and the nine at Ulysses that have been acquired as of sol 2000 (August 18, 2009). At the Tyrone “yellow” soil, the blue-to-red (432 to 753 nm) spectral slope decreased after roughly 175 sols of exposure to the martian surface, as described by Wang et al. (2008, JGR, 114, 461). This spectral change is contrary to the “reddening” that would be expected from dust deposition, but could be consistent with dehydration pathways of certain ferric sulfates, such as from copiapite to amorphous ferric sulfates or to rhomboclase (Wang et al., 2008, AGU). The Tyrone “yellow” soil also exhibits increased 535 nm and 803 nm band depths with time, which is further suggestive of a mineralogic change. Pancam spectra of Kit Carson appear to have changed similarly to those of Tyrone, with 535 nm and 864 nm absorptions developing after four

  6. Photoinduced formation of thiols in human hair.

    PubMed

    Fedorkova, M V; Brandt, N N; Chikishev, A Yu; Smolina, N V; Balabushevich, N G; Gusev, S A; Lipatova, V A; Botchey, V M; Dobretsov, G E; Mikhalchik, E V

    2016-11-01

    Raman, scanning electron, and optical microscopy of hair and spectrophotometry of soluble hair proteins are used to study the effect of UV-vis radiation on white hair. The samples of a healthy subject are irradiated using a mercury lamp and compared with non-irradiated (control) hair. The cuticle damage with partial exfoliation is revealed with the aid of SEM and optical microscopy of semifine sections. Gel filtration chromatography shows that the molecular weight of soluble proteins ranges from 5 to 7kDa. Absorption spectroscopy proves an increase in amount of thiols in a heavier fraction of the soluble proteins of irradiated samples under study. Raman data indicate a decrease in the amount of SS and CS bonds in cystines and an increase in the amount of SH bonds due to irradiation. Such changes are more pronounced in peripheral regions of hair. Conformational changes of hair keratins presumably related to the cleavage of disulfide bonds, follow from variations in amide I and low-frequency Raman bands. An increase in the content of thiols in proteins revealed by both photometric data on soluble proteins and Raman microspectroscopy of hair cuts can be used to develop a protocol of the analysis of photoinduced hair modification.

  7. Monitoring small changes in blood hematocrit using phase sensitive spectral domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Manne, Venu G. R.; Manapuram, Ravi Kiran; Sudheendran, Narendran; Larin, Kirill V.

    2010-02-01

    A new method for monitoring ultra-small changes in blood hematocrit (~0.2%) based on measurement of refractive index changes in vitro using Phase Sensitive Spectral Domain Optical Coherence Tomography modality (PhS-SDOCT) is introduced. The developed system has an axial resolution of ~8 μm, phase sensitivity of +/-0.01 radians, imaging depth of 3.4 +/- 0.01 mm in air, and image acquisition speed of 29 kHz. The experimental accuracy for monitoring refractive index changes as a function of hematocrit level in blood is found to be +/-1.5x10-4 (+/-0.2%). Obtained results indicate that the PhS-SDOCT can be used to monitor ultra-small changes in the hematocrit and in vitro and, potentially, in tissue blood vessels in vivo.

  8. Photoinduced conformational changes in DNA by poly(vinyl alcohol) carrying a malachite green moiety for protecting DNA against attack by nuclease.

    PubMed

    Uda, Ryoko M; Matsui, Takashi

    2015-11-14

    Light is a highly advantageous means of specific cell targeting. Though targeted gene delivery is an important characteristic of an ideal delivery vehicle, there has been little effort to develop a photoresponsive vector. Among nonviral vectors, cationic substances interact effectively with negatively charged DNA. With this property in mind, we designed copolymers of poly(vinyl alcohol) carrying a malachite green moiety (PVAMG) with different molecular weights. Though PVAMG has no affinity for DNA in the absence of light, it undergoes photoionization in the presence of light to afford cationic DNA binding sites. The DNA-PVAMG complex was investigated with respect to DNA conformational changes and its protective nature, which are important properties for nonviral vectors. PVAMG irradiation promoted DNA conformational transitions from coils to partial globules to compacted globules. The complex had a protective effect against DNase I after PVAMG irradiation, while DNA was degraded under dark conditions. The effect on DNA transition and the protective nature were sensitive to the molecular weight of PVAMG. The data regarding binding constants and binding mode provided insight into the structure of the DNA-PVAMG complex. To withstand DNase I attacks, complexation results in the compaction of DNA, which is further covered with PVAMG.

  9. Paleo-productivity changes revealed by spectral analysis performed on coccoliths assemblages

    NASA Astrophysics Data System (ADS)

    Palumbo, Eliana; Ornella Amore, Filomena; Perugia, Carmen

    2010-05-01

    Several climate changes occurred over geological time at different time-scales. Spectral analyses performed on paleo-climate data suggested that these cyclicities verify irregularly into time-space domain. Paleo-climate oscillations occur with high or low frequencies dues to the oscillation of the major orbital parameters (characterized by low frequencies and high period) and some minor high-frequencies events. During last years, analyses on frequencies domain have been performed also on coccoliths assemblages. Coccolithophores are a special phytoplankton group living today at all latitude regions within the photic zone (0-200 m of depth) (Winter & Siesser, 1994). They are sensitive indicators of environmental conditions because they directly depend on temperature, salinity and nutrients as well as the availability of sunlight (McIntyre and Bé, 1967; Giradeau et al., 1993; Winter & Siesser, 1994; Baumann & Freitag, 2004). Therefore coccolithophores quickly respond to fluctuations in climate as well as changes in surface-water conditions (Baumann & Freitag, 2004). Thus coccoliths can be clearly used as paleo-climate data because of their power of recordering and amplifying climatic change signals. In addition, primary productivity depends on the amount of insolation received by Earth surface. In this study Sun insolation has been calculated in terms of intensity and energy, in order to compare them with maximum productivity activity. Precession controls sun intensity insolation, while the energy is controlled by obliquity. Thus, the intensity depends on the duration of the insolation,while the energy is connected to the amount of insolation (Berger, 1978; Loutre et al., 2004; Huybers, 2006). In this study, spectral analyses have been performed on coccoliths data with the result of individuating high and low frequencies content in productivity signals. Auto-spectral and cross-spectral analyses have been performed through Matlab software using several available

  10. Photoinduced Electron Transfer Process Visualized on Single Silver Nanoparticles.

    PubMed

    Lei, Gang; Gao, Peng Fei; Yang, Tong; Zhou, Jun; Zhang, Hong Zhi; Sun, Shan Shan; Gao, Ming Xuan; Huang, Cheng Zhi

    2017-02-28

    Understanding the photoinduced electron transfer (PET) mechanism is vital to improving the photoelectric conversion efficiency for solar energy materials and photosensitization systems. Herein, we visually demonstrate the PET process by real-time monitoring the photoinduced chemical transformation of p-aminothiophenol (p-ATP), an important SERS signal molecule, to 4,4'-dimercaptoazobenzene on single silver nanoparticles (AgNPs) with a localized surface plasmon resonance (LSPR) spectroscopy coupled dark-field microscopy. The bidirectional LSPR scattering spectral shifts bathochromically at first and hypsochromically then, which are caused by the electron transfer delay of p-ATP, disclose the PET path from p-ATP to O2 through AgNPs during the reaction, and enable us to digitalize the corresponding electron loss and gain on the surface of AgNP at different time periods. This visualized PET process could provide a simple and efficient approach to explore the nature of PET and help to interpret the SERS mechanism in terms of p-ATP.

  11. Spectral indices for remote sensing of phytomass and deciduous shrub changes in Alaskan arctic tundra

    NASA Astrophysics Data System (ADS)

    Kushida, K.; Hobara, S.; Tsuyuzaki, S.; Watanabe, M.; Harada, K.; Kim, Y.; Shaver, G. R.; Fukuda, M.

    2010-12-01

    The relationships between spectral indices, phytomass, and plant functional types were determined by using field observations of a moist acidic tundra (MAT) and a moist non-acidic tundra (MNT) in the Toolik Lake Long Term Ecological Research (LTER) site and a sedge-shrub tundra (SS) in the Arctic National Wildlife Refuge, Alaska, USA. For the MAT and MNT observations, among aboveground phytomass, aboveground vascular phytomass, and vascular plant green phytomass, vascular plant green phytomass was the most sensitive to an exponential function of the normalized difference vegetation index (NDVI). The coefficient of determination (R2) was 0.73. Vascular plant carbon and nitrogen were estimated with exponential functions of NDVI (R2 of 0.57 and 0.53, respectively). For the MAT, MNT, and SS observations, vascular plant green phytomass was more strongly correlated with an exponential function of NDVI (ENDVI, R2 of 0.62) than any other spectral indices. On the other hand, for deciduous shrub green phytomass, the strongest correlation was with a product of an exponential function of NDVI and a spectral index (MIR - RED)/(MIR + RED) (DSSI, R2 of 0.60). Here, MIR and RED denote the bands with wavelengths 2.09-2.35 and 0.63-0.69 µm, respectively. As a result of a regression analysis, 41% of the ENDVI variance and 60% of the DSSI variance were explained by deciduous shrub green phytomass. Up to 38% of the ENDVI variance and up to 10% of the DSSI variance were explained by green phytomass of evergreen shrubs and graminoids, and phytomass of mosses/lichens. These spectral indices were applicable to evaluating tundra plant community changes.

  12. Photoinduced magnetic force between nanostructures

    NASA Astrophysics Data System (ADS)

    Guclu, Caner; Tamma, Venkata Ananth; Wickramasinghe, Hemantha Kumar; Capolino, Filippo

    2015-12-01

    Photoinduced magnetic force between nanostructures, at optical frequencies, is investigated theoretically. Till now optical magnetic effects were not used in scanning probe microscopy because of the vanishing natural magnetism with increasing frequency. On the other hand, artificial magnetism in engineered nanostructures led to the development of measurable optical magnetism. Here two examples of nanoprobes that are able to generate strong magnetic dipolar fields at optical frequency are investigated: first, an ideal magnetically polarizable nanosphere and then a circular cluster of silver nanospheres that has a looplike collective plasmonic resonance equivalent to a magnetic dipole. Magnetic forces are evaluated based on nanostructure polarizabilities, i.e., induced magnetic dipoles, and magnetic-near field evaluations. As an initial assessment on the possibility of a magnetic nanoprobe to detect magnetic forces, we consider two identical magnetically polarizable nanoprobes and observe magnetic forces on the order of piconewtons, thereby bringing it within detection limits of conventional atomic force microscopes at ambient pressure and temperature. The detection of magnetic force is a promising method in studying optical magnetic transitions that can be the basis of innovative spectroscopy applications.

  13. Photoinduced toxicity of engineered nanomaterials

    NASA Astrophysics Data System (ADS)

    Jones, Philip Scott

    Engineered nanomaterials including metal, metal oxide and carbon based nanomaterials are extensively used in a wide variety of applications to the extent that their presence in the environment is expected to increase dramatically over the next century. These nanomaterials may be photodegraded by solar radiation and thereby release metal ions into the environment that can produce cytotoxic and genotoxic effects. Photoinduced toxicity experiments are performed exposing human lung epithelial carcinoma cells [H1650] to engineered semiconductor nanoparticles such as CdSe quantum dots and ZnO nanoparticles after exposure to 3, 6, and 9 hours of solar simulated radiation. Cytotoxicity and genotoxicity of the metal ions are evaluated using ZnSO4 and CdCl2 solutions for the MTT assay and Comet assay respectively. The objective of the dissertation is to obtain quantitative information about the environmental transformation of engineered nanomaterials and their mechanism of toxicity. This information is critical for addressing the environmental health and safety risks of engineered nanomaterials to workers, consumers and the environment.

  14. Novel mechanism of photoinduced reversible phase transitions in molecule-based magnets.

    PubMed

    Kawamoto, T; Asai, Y; Abe, S

    2001-01-08

    A novel microscopic mechanism of bidirectional structural changes is proposed for the photoinduced magnetic phase transition in Co-Fe Prussian blue analogs on the basis of ab initio quantum chemical cluster calculations. It is shown that the local potential energies of various spin states of Co are sensitive to the number of nearest neighbor Fe vacancies. As a result, the forward and backward structural changes are most readily initiated by excitation of different local regions by different photons. This mechanism suggests an effective strategy to realize photoinduced reversible phase transitions in a general system consisting of two local components.

  15. Static and dynamic photoinduced magnetic effects in yttrium-iron garnet lightly doped with barium ions

    SciTech Connect

    Vorob'eva, N. V. Khalilov, R. Z.

    2012-04-15

    In yttrium-iron garnet lightly doped with barium, direct measurements of the photoinduced changes in magnetostrictive strains disagree with those in magnetostriction constants at 78-100 K. This is attributed to a considerable photoinduced modification of the initial state in this sample due to a redistribution of the charge (during illumination) between cations of the ferromagnetic octahedral sublattice. In the same sample, the temperature dependence of the photoinduced disaccomodation of magnetic permeability characterizing the initial demagnetized state is measured and calculated. A change in the electron mechanism of the phenomenon during the transition to room temperature is shown. The conclusion about the promising prospects for using such samples for remagnetization by light is advanced.

  16. Unsupervised change detection in a particular vegetation land cover type using spectral angle mapper

    NASA Astrophysics Data System (ADS)

    Renza, Diego; Martinez, Estibaliz; Molina, Iñigo; Ballesteros L., Dora M.

    2017-04-01

    This paper presents a new unsupervised change detection methodology for multispectral images applied to specific land covers. The proposed method involves comparing each image against a reference spectrum, where the reference spectrum is obtained from the spectral signature of the type of coverage you want to detect. In this case the method has been tested using multispectral images (SPOT5) of the community of Madrid (Spain), and multispectral images (Quickbird) of an area over Indonesia that was impacted by the December 26, 2004 tsunami; here, the tests have focused on the detection of changes in vegetation. The image comparison is obtained by applying Spectral Angle Mapper between the reference spectrum and each multitemporal image. Then, a threshold to produce a single image of change is applied, which corresponds to the vegetation zones. The results for each multitemporal image are combined through an exclusive or (XOR) operation that selects vegetation zones that have changed over time. Finally, the derived results were compared against a supervised method based on classification with the Support Vector Machine. Furthermore, the NDVI-differencing and the Spectral Angle Mapper techniques were selected as unsupervised methods for comparison purposes. The main novelty of the method consists in the detection of changes in a specific land cover type (vegetation), therefore, for comparison purposes, the best scenario is to compare it with methods that aim to detect changes in a specific land cover type (vegetation). This is the main reason to select NDVI-based method and the post-classification method (SVM implemented in a standard software tool). To evaluate the improvements using a reference spectrum vector, the results are compared with the basic-SAM method. In SPOT5 image, the overall accuracy was 99.36% and the κ index was 90.11%; in Quickbird image, the overall accuracy was 97.5% and the κ index was 82.16%. Finally, the precision results of the method are

  17. Heat-induced changes to lipid molecular structure in Vimy flaxseed: Spectral intensity and molecular clustering

    NASA Astrophysics Data System (ADS)

    Yu, Peiqiang; Damiran, Daalkhaijav

    2011-06-01

    Autoclaving was used to manipulate nutrient utilization and availability. The objectives of this study were to characterize any changes of the functional groups mainly associated with lipid structure in flaxseed ( Linum usitatissimum, cv. Vimy), that occurred on a molecular level during the treatment process using infrared Fourier transform molecular spectroscopy. The parameters included lipid CH 3 asymmetric (ca. 2959 cm -1), CH 2 asymmetric (ca. 2928 cm -1), CH 3 symmetric (ca. 2871 cm -1) and CH 2 symmetric (ca. 2954 cm -1) functional groups, lipid carbonyl C dbnd O ester group (ca. 1745 cm -1), lipid unsaturation group (CH attached to C dbnd C) (ca. 3010 cm -1) as well as their ratios. Hierarchical cluster analysis (CLA) and principal components analysis (PCA) were conducted to identify molecular spectral differences. Flaxseed samples were kept raw for the control or autoclaved in batches at 120 °C for 20, 40 or 60 min for treatments 1, 2 and 3, respectively. Molecular spectral analysis of lipid functional group ratios showed a significant decrease ( P < 0.05) in the CH 2 asymmetric to CH 3 asymmetric stretching band peak intensity ratios for the flaxseed. There were linear and quadratic effects ( P < 0.05) of the treatment time from 0, 20, 40 and 60 min on the ratios of the CH 2 asymmetric to CH 3 asymmetric stretching vibration intensity. Autoclaving had no significant effect ( P > 0.05) on lipid carbonyl C dbnd O ester group and lipid unsaturation group (CH attached to C dbnd C) (with average spectral peak area intensities of 138.3 and 68.8 IR intensity units, respectively). Multivariate molecular spectral analyses, CLA and PCA, were unable to make distinctions between the different treatment original spectra at the CH 3 and CH 2 asymmetric and symmetric region (ca. 2988-2790 cm -1). The results indicated that autoclaving had an impact to the mid-infrared molecular spectrum of flaxseed to identify heat-induced changes in lipid conformation. A future study

  18. Spectral Changes in Metal Halide and High-pressure Sodium Lamps Equipped with Electronic Dimming

    NASA Technical Reports Server (NTRS)

    Bubenheim, David L.; Sargis, Raman; Wilson, David

    1995-01-01

    Electronic dimming of high-intensity discharge lamps offers control of photosynthetic photon flux (PPF) but is often characterized as causing significant spectral changes. Growth chambers with 400-W metal halide (MH) and high-pressure sodium (HPS) lamps were equipped with a dimmer system using silicon-controlled rectifiers (SCR) as high-speed switches. Phase control operation turned the line power off for some period of the alternating current cycle. At full power, the electrical input to HPS and MH lamps was 480 W (root mean squared) and could be decreased to 267 W and 428 W, respectively, before the arc was extinguished. Concomitant with this decrease in input power, PPF decreased by 60% in HPS and 50% in MH. The HPS lamp has characteristic spectral peaks at 589 and 595 nm. As power to the HPS lamps was decreased, the 589-nm peak remained constant while the 595-nm peak decreased, equaling the 589-nm peak at 345-W input, and the 589-nm peak was almost absent at 270-W input. The MH lamp has a broader spectral output but also has a peak at 589 nm and another smaller peak at 545 nm. As input power to the MH lamps decreased, the peak at 589 diminished to equal the 545-nm peak. As input power approached 428 W, the 589-nm peak shifted to 570 nm. While the spectrum changed as input power was decreased in the MH and HPS lamps, the phytochrome equilibrium ratio (P(sub fr):P(sub tot)) remains unchanged for both lamp types.

  19. Arsenic- and selenium-induced changes in spectral reflectance and morphology of soybean plants

    USGS Publications Warehouse

    Milton, N.M.; Ager, C.M.; Eiswerth, B.A.; Power, M.S.

    1989-01-01

    Soybean (Glycine max) plants were grown in hydroponic solutions treated with high concentrations of either arsenic or selenium. Spectral reflectance changes in arsenic-dosed plants included a shift to shorter wavelengths in the long-wavelength edge of the chlorophyll absorption band centered at 680 nm (the red edge) and higher reflectance in the 550-650 nm region. These results are consistent with vegetation reflectance anomalies observed in previous greenhouse experiments and in airborne radiometer studies. The selenium-dosed plants contrast, exhibited a shift to longer wavelengths of the red edge and lower reflectance between 550 nm and 650 wh when compared with control plants. Morphological effects of arsenic uptake included lower overall biomass, stunted and discolored roots, and smaller leaves oriented more vertically than leaves of control plants. Selenium-dosed plants also displayed morphological changes, but root and leaf biomass were less affected than were those of arsenic-dosed plants when compared to control plants. ?? 1989.

  20. Photoinduced modulation and relaxation characteristics in LaAlO3/SrTiO3 heterointerface

    PubMed Central

    Jin, K. X.; Lin, W.; Luo, B. C.; Wu, T.

    2015-01-01

    We report the modulation and relaxation characteristics in the two-dimensional electron gas system at LaAlO3/SrTiO3 heterointerface induced by the ultraviolet light illumination (365 nm). The suppression of Kondo effect at the interface illuminated by the light originates from the light irradiation-induced decoherence effect of localized states. It is interesting to note that the persistent and transient photoinduced effects are simultaneously observed and the photoinduced maximum change values in resistance are 80.8% and 51.4% at T = 20 K, respectively. Moreover, the photoinduced relaxation processes after the irradiation are systematically analyzed using the double exponential model. These results provide the deeper understanding of the photoinduced effect and the experimental evidence of tunable Kondo effect in oxides-based two-dimensional electron gas systems. PMID:25739889

  1. Photoinduced bimolecular electron transfer kinetics in small unilamellar vesicles

    SciTech Connect

    Choudhury, Sharmistha Dutta; Kumbhakar, Manoj; Nath, Sukhendu; Pal, Haridas

    2007-11-21

    Photoinduced electron transfer (ET) from N,N-dimethylaniline to some coumarin derivatives has been studied in small unilamellar vesicles (SUVs) of the phospholipid, DL-{alpha}-dimyristoyl-phosphatidylcholine, using steady-state and time-resolved fluorescence quenching, both below and above the phase transition temperature of the vesicles. The primary interest was to examine whether Marcus inversion [H. Sumi and R. A. Marcus, J. Chem. Phys. 84, 4894 (1986)] could be observed for the present ET systems in these organized assemblies. The influence of the topology of SUVs on the photophysical properties of the reactants and consequently on their ET kinetics has also been investigated. Absorption and fluorescence spectral data of the coumarins in SUVs and the variation of their fluorescence decays with temperature indicate that the dyes are localized in the bilayer of the SUVs. Time-resolved area normalized emission spectra analysis, however, reveals that the dyes are distributed in two different microenvironments in the SUVs, which we attribute to the two leaflets of the bilayer, one toward bulk water and the other toward the inner water pool. The microenvironments in the two leaflets are, however, not indicated to be that significantly different. Time-resolved anisotropy decays were biexponential for all the dyes in SUVs, and this has been interpreted in terms of the compound motion model according to which the dye molecules can experience a fast wobbling-in-cone type of motion as well as a slow overall rotating motion of the cone containing the molecule. The expected bimolecular diffusion-controlled rates in SUVs, as estimated by comparing the microviscosities in SUVs (determined from rotational correlation times) and that in acetonitrile solution, are much slower than the observed fluorescence quenching rates, suggesting that reactant diffusion (translational) does not play any role in the quenching kinetics in the present systems. Accordingly, clear inversions are

  2. The impact of changing night vision goggle spectral response on night vision imaging system lighting compatibility

    NASA Astrophysics Data System (ADS)

    Task, Harry L.; Marasco, Peter L.

    2004-09-01

    The defining document outlining night-vision imaging system (NVIS) compatible lighting, MIL-L-85762A, was written in the mid 1980's, based on what was then the state of the art in night vision and image intensification. Since that time there have been changes in the photocathode sensitivity and the minus-blue coatings applied to the objective lenses. Specifically, many aviation night-vision goggles (NVGs) in the Air Force are equipped with so-called "leaky green" or Class C type objective lens coatings that provide a small amount of transmission around 545 nanometers so that the displays that use a P-43 phosphor can be seen through the NVGs. However, current NVIS compatibility requirements documents have not been updated to include these changes. Documents that followed and replaced MIL-L-85762A (ASC/ENFC-96-01 and MIL-STD-3009) addressed aspects of then current NVIS technology, but did little to change the actual content or NVIS radiance requirements set forth in the original MIL-L-85762A. This paper examines the impact of spectral response changes, introduced by changes in image tube parameters and objective lens minus-blue filters, on NVIS compatibility and NVIS radiance calculations. Possible impact on NVIS lighting requirements is also discussed. In addition, arguments are presented for revisiting NVIS radiometric unit conventions.

  3. Photoinduced phase transition in tetrathiafulvalene- p -chloranil observed in femtosecond reflection spectroscopy

    NASA Astrophysics Data System (ADS)

    Okamoto, H.; Ishige, Y.; Tanaka, S.; Kishida, H.; Iwai, S.; Tokura, Y.

    2004-10-01

    Photoinduced transitions from ionic (I) to neutral (N) and neutral (N) to ionic (I) phases in an organic charge transfer (CT) complex, tetrathiafulvalene- p -chloranil (TTF-CA), were investigated by femtosecond pump-probe reflection spectroscopy. Transient reflectivity changes of the intramolecular transition band of TTF sensitive to the degree of CT between a donor molecule of TTF and an acceptor molecule of CA are measured as a function of excitation energy, excitation density, and temperature. By adopting the multilayer model for the analysis of the obtained transient reflectivity spectra, we have derived the time characteristics of amounts and spatial distributions of photoinduced N(I) states in the I(N) phase. The results reveal that the I to N(IN) transition induced by the resonant excitation of the CT band at 4K is composed of three processes; (1) formation of a confined one-dimensional (1D) N domain, that is, a sequence of D0A0 pairs, just after the photoexcitation, (2) multiplication of the 1D N domains to the semimacroscopic N states up to 20ps within the absorption depth of the excitation light, and (3) proceeding of the IN transition along the direction normal to the sample surface. At 77K near the NI transition temperature (Tc=81K) , the size of the 1D N domain initially produced is enlarged and its multiplication process is strongly enhanced. When the excitation energy is increased, the initial photoproduct is changed from the confined 1D N domain to the positively and negatively charged N states. The spatial size of the latter is considerably larger than that of the former, indicating that the introduction of charge carriers makes the neighboring I state strongly unstable. The dynamics of the photoinduced N to I(NI) transition has also been investigated. The 1D I domains are initially produced by lights, however, they decay within 20ps even if the density of the I domains is increased. The results demonstrate that there is a clear difference of the

  4. Artificial light pollution: are shifting spectral signatures changing the balance of species interactions?

    PubMed Central

    Davies, Thomas W; Bennie, Jonathan; Inger, Richard; Ibarra, Natalie Hempel; Gaston, Kevin J

    2013-01-01

    Technological developments in municipal lighting are altering the spectral characteristics of artificially lit habitats. Little is yet known of the biological consequences of such changes, although a variety of animal behaviours are dependent on detecting the spectral signature of light reflected from objects. Using previously published wavelengths of peak visual pigment absorbance, we compared how four alternative street lamp technologies affect the visual abilities of 213 species of arachnid, insect, bird, reptile and mammal by producing different wavelength ranges of light to which they are visually sensitive. The proportion of the visually detectable region of the light spectrum emitted by each lamp was compared to provide an indication of how different technologies are likely to facilitate visually guided behaviours such as detecting objects in the environment. Compared to narrow spectrum lamps, broad spectrum technologies enable animals to detect objects that reflect light over more of the spectrum to which they are sensitive and, importantly, create greater disparities in this ability between major taxonomic groups. The introduction of broad spectrum street lamps could therefore alter the balance of species interactions in the artificially lit environment. PMID:23505141

  5. Observations of Solar Spectral Irradiance Change During Cycle 22 from NOAA-9 SBUV/2

    NASA Technical Reports Server (NTRS)

    DeLand, Matthew T.; Cebula, Richard P.; Hilsenrath, Ernest

    2003-01-01

    The NOM-9 Solar Backscatter Ultraviolet, model 2 (SBUV/2) instrument is one of a series of instruments providing daily solar spectral irradiance measurements in the middle and near ultraviolet since 1978. The SBUV/2 instruments are primarily designed to measure stratospheric profile and total column ozone, using the directional albedo as the input to the ozone processing algorithm. As a result, the SBUV/2 instrument does not have onboard monitoring of all time-dependent response changes. We have applied internal comparisons and vicarious (external) comparisons to determine the long-term instrument characterization for NOAA-9 SBUV/2 to derive accurate solar spectral irradiances from March 1985 to May 1997 spanning two solar cycle minima with a single instrument. The NOAA-9 data show an amplitude of 9.3(+/- 2.3)% (81-day averaged) at 200-205 nm for solar cycle 22. This is consistent with the result of (Delta)F(sub 200-205) = 8.3(+/- 2.6)% for cycle 21 from Nimbus-7 SBUV and (Delta)F(sub 200-205) = 10(+/- 2)% (daily values) for cycle 23 from UARS SUSIM. NOAA-9 data at 245-250 nm show a solar cycle amplitude of (Delta)F(sub 245-250) = 5.7(+/- 1.8)%. NOAA-9 SBUV/2 data can be combined with other instruments to create a 25-year record of solar UV irradiance.

  6. Artificial light pollution: are shifting spectral signatures changing the balance of species interactions?

    PubMed

    Davies, Thomas W; Bennie, Jonathan; Inger, Richard; de Ibarra, Natalie Hempel; Gaston, Kevin J

    2013-05-01

    Technological developments in municipal lighting are altering the spectral characteristics of artificially lit habitats. Little is yet known of the biological consequences of such changes, although a variety of animal behaviours are dependent on detecting the spectral signature of light reflected from objects. Using previously published wavelengths of peak visual pigment absorbance, we compared how four alternative street lamp technologies affect the visual abilities of 213 species of arachnid, insect, bird, reptile and mammal by producing different wavelength ranges of light to which they are visually sensitive. The proportion of the visually detectable region of the light spectrum emitted by each lamp was compared to provide an indication of how different technologies are likely to facilitate visually guided behaviours such as detecting objects in the environment. Compared to narrow spectrum lamps, broad spectrum technologies enable animals to detect objects that reflect light over more of the spectrum to which they are sensitive and, importantly, create greater disparities in this ability between major taxonomic groups. The introduction of broad spectrum street lamps could therefore alter the balance of species interactions in the artificially lit environment.

  7. Age-Associated Changes in the Spectral and Statistical Parameters of Surface Electromyogram of Tibialis Anterior

    PubMed Central

    2016-01-01

    Age-related neuromuscular change of Tibialis Anterior (TA) is a leading cause of muscle strength decline among the elderly. This study has established the baseline for age-associated changes in sEMG of TA at different levels of voluntary contraction. We have investigated the use of Gaussianity and maximal power of the power spectral density (PSD) as suitable features to identify age-associated changes in the surface electromyogram (sEMG). Eighteen younger (20–30 years) and 18 older (60–85 years) cohorts completed two trials of isometric dorsiflexion at four different force levels between 10% and 50% of the maximal voluntary contraction. Gaussianity and maximal power of the PSD of sEMG were determined. Results show a significant increase in sEMG's maximal power of the PSD and Gaussianity with increase in force for both cohorts. It was also observed that older cohorts had higher maximal power of the PSD and lower Gaussianity. These age-related differences observed in the PSD and Gaussianity could be due to motor unit remodelling. This can be useful for noninvasive tracking of age-associated neuromuscular changes. PMID:27610379

  8. Imaging of photoinduced tautomerism in single porphyrin molecules

    NASA Astrophysics Data System (ADS)

    Jäger, Regina; Chizhik, Anna M.; Chizhik, Alexey I.; Mack, Hans-Georg; Lyubimtsev, Alexey; Hanack, Michael; Meixner, Alfred J.

    2011-10-01

    In this work we present our new experimental and theoretical results upon investigations of the photoinduced tautomerism processes of single metal-free porphyrin-type molecules. During tautomerization a molecule changes its structure, therefore the excitation transition dipole moment (TDM) of the molecule changes its orientation. Using confocal microscopy in combination with azimuthally and radially polarized laser beams we are able to determine the orientation of the TDM as well as the orientation of a single molecule itself. In the case of tautomerism we are able to visualize this process and even the involved isomers separately. The study first focuses on two symmetrical compounds: a phthalocyanine and a porphyrin. Additionally, differences of the single molecules embedded in a polymer matrix or just spin-coated on a glass cover slide and under nitrogen flow are investigated. In the latter case we observe a higher frequency of the change of the TDM orientation. The experimental studies are supplemented by quantum chemical calculations. Variations of the molecular substituents, the environment and excitation wavelength can give new insights into the excited-state tautomerism process of a single molecule. We also introduce some suggestions for future experiments to support the understanding of the photoinduced tautomerism.

  9. Dual absorption spectral changes by light-triggered shuttling in bistable [2]rotaxanes with non-destructive readout.

    PubMed

    Zhan, Tian-Guang; Yun, Meng-Yan; Lin, Jia-Le; Yu, Xin-Yao; Zhang, Kang-Da

    2016-12-01

    Light-triggered photoisomerization of the azobenzene (AB) unit in bistable [2]rotaxanes can cause the shuttling of the macrocycle on the dumbbell, resulting in distinctive dual spectral variation characteristics: (1) the spectral change of the photochromic unit and (2) the variation of the charge-transfer band. By employing the CT bond region as an output signal, non-destructive readout of optical information could be achieved.

  10. Relation Between Changes in Pigments' Spectral Properties and Structural Distortions of Pigment Protein Complexes (abstract)

    NASA Astrophysics Data System (ADS)

    Stoitchkova, Katerina; Andreeva, Atanaska; Busheva, Mira

    2009-04-01

    Scientists continue to investigate photosynthesis-nature's process to efficiently regulate and store energy. To explore the mechanisms of regulation we used fluorescence, resonance Raman spectroscopy, and biochemical preparative methods. For detailed analysis we applied decomposition of the low temperature steady-state fluorescence spectra. This allowed us to estimate the emission of distinct pigment protein complexes (PPC) and evaluate the fluorescence of various aggregation forms of the main light harvesting complex (LHCII), which plays a major role in the studied mechanisms. Resonance Raman spectroscopy revealed with precision the relation between changes in pigments' spectral properties and structural distortions of PPC. It was shown that aggregation of LHCII led to out-of-plane distortion, not only of neoxanthin, but also of lutein molecules. This was enhanced when the complex was embedded in thylakoid membranes (TM). It was suggested that lutein molecules are more closely related to the process of aggregation of LHCII in TM than neoxanthin.

  11. An investigation of spectral change as influenced by irrigation and evapotranspiration volume estimation in western Nebraska

    USGS Publications Warehouse

    Seevers, P.M.; Sadowski, F.C.; Lauer, D.T.

    1990-01-01

    Retrospective satellite image data were evaluated for their ability to demonstrate the influence of center-pivot irrigation development in western Nebraska on spectral change and climate-related factors for the region. Periodic images of an albedo index and a normalized difference vegetation index (NDVI) were generated from calibrated Landsat multispectral scanner (MSS) data and used to monitor spectral changes associated with irrigation development from 1972 through 1986. The albedo index was not useful for monitoring irrigation development. For the NDVI, it was found that proportions of counties in irrigated agriculture, as discriminated by a threshold, were more highly correlated with reported ground estimates of irrigated agriculture than were county mean greenness values. A similar result was achieved when using coarse resolution Advanced Very High Resolution Radiometer (AVHRR) image data for estimating irrigated agriculture. The NDVI images were used to evaluate a procedure for making areal estimates of actual evapotranspiration (ET) volumes. Estimates of ET volumes for test counties, using reported ground acreages and corresponding standard crop coefficients, were correlated with the estimates of ET volume using crop coefficients scaled to NDVI values and pixel counts of crop areas. These county estimates were made under the assumption that soil water availability was unlimited. For nonirrigated vegetation, this may result in over-estimation of ET volumes. Ground information regarding crop types and acreages are required to derive the NDVI scaling factor. Potential ET, estimated with the Jensen-Haise model, is common to both methods. These results, achieved with both MSS and AVHRR data, show promise for providing climatologically important land surface information for regional and global climate models. ?? 1990 Kluwer Academic Publishers.

  12. Changes in foliar spectral reflectance and chlorophyll fluorescence of four temperate species following branch cutting.

    PubMed

    Richardson, Andrew D; Berlyn, Graeme P

    2002-05-01

    Spectral reflectance and chlorophyll fluorescence are rapid non-invasive methods that can be used to quantify plant stress. Because variation in ambient light (e.g., diurnal patterns of solar radiation) may have a confounding effect on these measurements, branches are often excised in the field and then measured under controlled conditions in the laboratory. We studied four temperate tree species (Abies balsamea (L.) Mill. (balsam fir), Betula papyrifera var. cordifolia (Regel) Fern. (paper birch), Picea rubens Sarg. (red spruce) and Sorbus americana Marsh. (mountain-ash)) to determine how quickly reflectance and fluorescence change following branch cutting. We hypothesized that conifer species, which have tough xeromorphic foliage, would exhibit changes more slowly than broadleaf species. Furthermore, we hypothesized that keeping broadleaf samples cool and moist would delay the onset of reflectance and fluorescence changes. In one set of experiments, we did not use any treatments to maintain the freshness of cut branches. During the first 12 h following cutting, changes in reflectance and fluorescence were slight for all species. Two or 3 days after branch cutting, the two conifers still showed only small changes in the ratio of variable to maximum fluorescence (Fv/Fm) and most reflectance indices, whereas paper birch and mountain-ash showed larger and more rapid declines in Fv/Fm and most reflectance indices. We attribute these declines to loss of water. As a consequence of xeromorphic leaf structure, the conifers were better able to minimize water loss than the two broadleaf species. In another experiment, paper birch that had been kept cool and moist after cutting showed only slight changes in fluorescence and reflectance, even after 3 days, indicating that with careful handling the time interval between collection and measurement of reflectance and fluorescence of many broadleaf specimens can be extended to several days. We conclude that measurements of

  13. Spectral and temporal changes to speech produced in the presence of energetic and informational maskers.

    PubMed

    Cooke, Martin; Lu, Youyi

    2010-10-01

    Talkers change the way they speak in noisy conditions. For energetic maskers, speech production changes are relatively well-understood, but less is known about how informational maskers such as competing speech affect speech production. The current study examines the effect of energetic and informational maskers on speech production by talkers speaking alone or in pairs. Talkers produced speech in quiet and in backgrounds of speech-shaped noise, speech-modulated noise, and competing speech. Relative to quiet, speech output level and fundamental frequency increased and spectral tilt flattened in proportion to the energetic masking capacity of the background. In response to modulated backgrounds, talkers were able to reduce substantially the degree of temporal overlap with the noise, with greater reduction for the competing speech background. Reduction in foreground-background overlap can be expected to lead to a release from both energetic and informational masking for listeners. Passive changes in speech rate, mean pause length or pause distribution cannot explain the overlap reduction, which appears instead to result from a purposeful process of listening while speaking. Talkers appear to monitor the background and exploit upcoming pauses, a strategy which is particularly effective for backgrounds containing intelligible speech.

  14. Biotinylated Platinum(II) Ferrocenylterpyridine Complexes for Targeted Photoinduced Cytotoxicity.

    PubMed

    Mitra, Koushambi; Shettar, Abhijith; Kondaiah, Paturu; Chakravarty, Akhil R

    2016-06-06

    Biotinylated platinum(II) ferrocenylterpyridine (Fc-tpy) complexes [Pt(Fc-tpy)(L(1))]Cl (1) and [Pt(Fc-tpy)(L(2))]Cl (2), where HL(1) and HL(2) are biotin-containing ligands, were prepared, and their targeted photoinduced cytotoxic effect in cancer cells over normal cells was studied. A nonbiotinylated complex, [Pt(Fc-tpy)(L(3))]Cl (3), was prepared as a control to study the role of the biotin moiety in cellular uptake properties of the complexes. Three platinum(II) phenylterpyridine (Ph-tpy) complexes, viz., [Pt(Ph-tpy)(L(1))]Cl (4), [Pt(Ph-tpy)(L(2))]Cl (5), and [Pt(Ph-tpy)(L(3))]Cl (6), were synthesized and explored to understand the role of a metal-bound Fc-tpy ligand over Ph-tpy as a photoinitiator. The Fc-tpy complexes displayed an intense absorption band near 640 nm, which was absent in their Ph-tpy analogues. The Fc-tpy complexes (1 mM in 0.1 M TBAP) showed an irreversible cyclic voltammetric anodic response of the Fc/Fc(+) couple near 0.25 V. The Fc-tpy complexes displayed photodegradation in red light of 647 nm involving the formation of a ferrocenium ion (Fc(+)) and reactive oxygen species (ROS). Photoinduced release of the biotinylated ligands was observed from spectral measurements, and this possibly led to the controlled generation of an active platinum(II) species, which binds to the calf-thymus DNA used for this study. The biotinylated photoactive Fc-tpy complexes showed significant photoinduced cytotoxicity, giving a IC50 value of ∼7 μM in visible light of 400-700 nm with selective uptake in BT474 cancer cells over HBL-100 normal cells. Furthermore, ferrocenyl complexes resulted in light-induced ROS-mediated apoptosis, as indicated by DCFDA, annexin V/FITC staining, and sub-G1 DNA content determined by fluorescent activated cell sorting analysis. The phenyl analogues 4 and 5 were photostable, served as DNA intercalators, and demonstrated selective cytotoxicity in the cancer cells, giving IC50 values of ∼4 μM.

  15. Photoinduced Birefringence in Azo-Dye Doped Polyurethane

    NASA Astrophysics Data System (ADS)

    Aleksejeva, J.; Gerbreders, A.; Reinfelde, M.; Teteris, J.

    2011-01-01

    In this report we describe a photoinduced birefringence in disperse red (DR1) azo-dye doped polyurethane films. DR1 dye molecules in these films are chemically bound with the polyurethane polymer's main chain. Under laser radiation the DR1 molecules experience the isomerization process; as a result, the dipole moment of such a molecule changes and they align in the presence of electric field. Photo-birefringence was induced by linearly polarized laser radiation (532 nm, 448 nm, 375 nm and 632.8 nm) in the films with various concentrations of DR1 dye. The photo-induced birefringence (PIBR) Δn was measured at 634 nm wavelength, and its dependences on the pumping beam wavelength and intensity were evaluated. The Δn relaxation was studied both in the dark and under light illumi-nation. In DR1-doped polyurethane films the holographic recording was performed using laser light radiation (532 nm). The profile of surface relief grating (SRG) was studied using AFM. The relationship between SRG formation and PIBR is discussed.

  16. Surfactant-directed synthesis of silver nanorods and characteristic spectral changes occurred by their morphology evolution

    NASA Astrophysics Data System (ADS)

    Zhang, Wen; Hu, Guansong; Zhang, Wanzhong; Qiao, Xueliang; Wu, Kai; Chen, Qingyuan; Cai, Yuchun

    2014-11-01

    Silver nanorods with different polydispersity were synthesized in the cetyltrimethylammonium bromide (CTAB) rod-shaped micelles by inducing the orientation growth of silver seeds and adjusting the volumes of CTAB. The reaction for the formation of silver nanorods had basically finished in 10 min. A suitable volume of CTAB (i.e., 15.0 mL of 0.1 M CTAB) is beneficial to obtain high-quality silver nanorods in the given reaction system. That is, the volume of added CTAB is a key factor to determine the polydispersity of the formed nanorods. The aging time plays a critical role in the morphology evolution of silver nanorods due to the oxidation of silver nanorods with Br-, O2 and the Ostwald ripening of the nanoparticles. As a result, the characteristic spectral changes occurred due to the morphology evolution of silver nanorods. The ablation in the top ends of the longer nanorods is often accompanied by the growth of some shorter nanorods and nanospheres. The size distribution of silver nanorods might be more uniform in the early aging stage. All the nanorods in the colloidal solution should turn into the near-spherical nanoparticles with larger sizes and thus the characteristic absorption should change to single peak centered at about 400 nm. Based on the research results, mathematical models are proposed for explaining the formation and morphology changes of silver nanorods. The morphology evolution of silver nanorods may be important and can be used as a reference for preparing silver nanorods, nanowires and other anisotropic nanomaterials.

  17. Chemical Detection Based on Adsorption-Induced and Photo-Induced Stresses in MEMS Devices

    SciTech Connect

    Datskos, P.G.

    1999-04-05

    Recently there has been an increasing demand to perform real-time in-situ chemical detection of hazardous materials, contraband chemicals, and explosive chemicals. Currently, real-time chemical detection requires rather large analytical instrumentation that are expensive and complicated to use. The advent of inexpensive mass produced MEMS (micro-electromechanical systems) devices opened-up new possibilities for chemical detection. For example, microcantilevers were found to respond to chemical stimuli by undergoing changes in their bending and resonance frequency even when a small number of molecules adsorb on their surface. In our present studies, we extended this concept by studying changes in both the adsorption-induced stress and photo-induced stress as target chemicals adsorb on the surface of microcantilevers. For example, microcantilevers that have adsorbed molecules will undergo photo-induced bending that depends on the number of absorbed molecules on the surface. However, microcantilevers that have undergone photo-induced bending will adsorb molecules on their surfaces in a distinctly different way. Depending on the photon wavelength and microcantilever material, the microcantilever can be made to bend by expanding or contracting the irradiated surface. This is important in cases where the photo-induced stresses can be used to counter any adsorption-induced stresses and increase the dynamic range. Coating the surface of the microstructure with a different material can provide chemical specificity for the target chemicals. However, by selecting appropriate photon wavelengths we can change the chemical selectivity due to the introduction of new surface states in the MEMS device. We will present and discuss our results on the use of adsorption-induced and photo-induced bending of microcantilevers for chemical detection.

  18. Transient electronic structure of the photoinduced phase of Pr0.7Ca0.3MnO3 probed with soft x-ray pulses

    SciTech Connect

    Rini, M.; Zhu, Y.; Wall, S.; Tobey, R. I.; Ehrke, H.; Garl, T.; Freeland, J. W.; Tomioka, Y.; Tokura, Y.; Cavalleri, A.; Schoenlein, R. W.

    2009-04-01

    We use time-resolved x-ray absorption near-edge structure spectroscopy to investigate the electronic dynamics associated with the photoinduced insulator-to-metal phase transition in the colossal magnetoresistive manganite Pr{sub 0.7}Ca{sub 0.3}MnO{sub 3}. Absorption changes at the O K and Mn L edges directly monitor the evolution of the density of unoccupied states in the transient photoinduced phase. We show that the electronic structure of the photoinduced phase is remarkably similar to that of the ferromagnetic metallic phase reached in related manganites upon cooling below the Curie temperature.

  19. Photoinduced processes in hybrid structures on the basis of TiO2 nanoparticles and CdSe/ZnS quantum dots

    NASA Astrophysics Data System (ADS)

    Kolesova, E. P.; Orlova, A. O.; Maslov, V. G.; Gun'ko, Yu. K.; Cleary, O.; Baranov, A. V.; Fedorov, A. V.

    2017-01-01

    The morphology of and photoinduced changes in the luminescent properties of hybrid structures on the basis of TiO2 nanoparticles and CdSe/ZnS quantum dots are studied. It is established that the morphology of the structures depends on the method of their formation and the type of stabilizer of the CdSe/ZnS surface. It is shown that a photoinduced decrease in the efficiency of nonradiative relaxation of the excitation in the quantum dots leads to an increase in the quantum yield of their luminescence and an increase in the efficiency of photoinduced charge transfer in hybrid structures.

  20. Seasonal changes in H/V spectral ratio at high-latitude seismic stations

    NASA Astrophysics Data System (ADS)

    Lee, R. F.; Abbott, R. E.; Knox, H. A.; Pancha, A.

    2014-12-01

    We present results demonstrating seasonal variations in the Horizontal-to-Vertical Spectral Ratio (HVSR) at high-latitude seismic stations. We analyze data from two sites at Poker Flat Research Range, near Fairbanks, Alaska. From the first site, we analyze 3 stations installed by Sandia National Labs (SNL) in a valley with marshy summer conditions. We also analyze the PASSCAL Instrument Center station PIC2, which is installed on rock approximately 3.2 km from the SNL stations. These stations continuously record data at 125 (SNL) and 200 (PIC2) samples per second. Seasonal changes in HVSR at high frequencies (> 20 Hz) appear to be caused by impedance contrasts between frozen and thawed ground. Thawed active layers are known to have slower shear-wave velocities than frozen layers or bedrock. An estimate of active layer thickness at each station is obtained from the quarter-wavelength approximation. We verify the accuracy of this technique by obtaining ground-truth measurements at the sites for both thickness and shear-wave velocity. We use physical probing for the thickness measurements and active-source Refraction-Microtremor (ReMi) surveys for the shear-wave velocities. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000

  1. Spectral and luminous efficacy change of high-power LEDs under different dimming methods

    NASA Astrophysics Data System (ADS)

    Gu, Yimin; Narendran, Nadarajah; Dong, Tianming; Wu, Huiying

    2006-08-01

    Dimming is an important and necessary feature for light sources used in general lighting applications. An experimental study was conducted to quantify the spectral and luminous efficacy change of high-power colored and pc-white LEDs under continuous current reduction (CCR) and pulse-width modulation (PWM) dimming schemes. For InGaN-based blue, green, and pc-white LEDs, the peak wavelength shifts were in opposite directions for the two dimming schemes. The peak wavelength showed a blue shift with increased current, most likely due to band filling and QCSE dominated effects. InGaN LEDs exhibited red shifts with increased duty cycle, which is dominated by junction heat. AlInGaP red LEDs show mainly thermal-induced red shift with increased current or duty cycle. In addition, the luminous efficacy was always higher for the CCR dimming scheme at dimmed levels, irrespective of the LED type. Keywords: Light-emitting diodes (LEDs), white LEDs, mixed-color white LEDs, pulse-width modulation (PWM), continuous current reduction (CCR), peak wavelength shift, luminous efficacy

  2. Long-Term and Progressive Changes in Rhesus Spectral Sensitivity after Low-Level Coherent Light (514 nm) Exposure).

    DTIC Science & Technology

    1981-12-01

    COVERED Long - term and Progressive changes in Rhesus Spectral Sensitivity after Low-level Coherent Ligh Technote 1978-1990 (514) Exposure 6. PERFORMING...recoverable with time or through alternative stimulation is also unknown. It seems plausible to us at the present time to entertain two hypotheses: first

  3. Spectral Reflectance and Vegetation Index Changes in Deciduous Forest Foliage Following Tree Removal: Potential for Deforestation Monitoring

    NASA Astrophysics Data System (ADS)

    Peng, D.; Hu, Y.; Li, Z.

    2016-05-01

    It is important to detect and quantify deforestation to guide strategic decisions regarding environment, socioeconomic development, and climate change. In the present study, we conducted a field experiment to examine spectral reflectance and vegetation index changes in poplar and locust tree foliage with different leaf area indices over the course of three sunny days, following tree removal from the canopy. The spectral reflectance of foliage from harvested trees was measured using an ASD FieldSpec Prospectroradiometer; synchronous meteorological data were also obtained. We found that reflectance in short-wave infrared and red-edge reflectance was more time sensitive after tree removal than reflectance in other spectral regions, and that the normalized difference water index (NDWI) and the red-edge chlorophyll index (CIRE) were the preferred indicators of these changes from several indices evaluated. Synthesized meteorological environments were found to influence water and chlorophyll contents after tree removal, and this subsequently changed the spectral canopy reflectance. Our results indicate the potential for such tree removal to be detected with NDWI or CIRE from the second day of a deforestation event.

  4. Wave spectral response to sudden changes in wind direction in finite-depth waters

    NASA Astrophysics Data System (ADS)

    Aijaz, Saima; Rogers, W. Erick; Babanin, Alexander V.

    2016-07-01

    The response of a wind-sea spectrum to sudden changes in wind directions of 180° and 90° is investigated. Numerical simulations using the third-generation wave spectral model SWAN have been undertaken at micro timescales of 30 s and fine spatial resolution of less than 10 m. The results have been validated against the wave data collected during the field campaign at Lake George, Australia. The newly implemented 'ST6' physics in the SWAN model has been evaluated using a selection of bottom-friction terms and the two available functions for the nonlinear energy transfer: (1) exact solution of the nonlinear term (XNL), and (2) discrete interactions approximation (DIA) that parameterizes the nonlinear term. Good agreement of the modelled data is demonstrated directly with the field data and through the known experimental growth curves obtained from the extensive Lake George data set. The modelling results show that of the various combinations of models tested, the ST6/XNL model provides the most reliable computations of integral and spectral wave parameters. When the winds and waves are opposing (180° wind turn), the XNL is nearly twice as fast in the aligning the young wind-sea with the new wind direction than the DIA. In this case, the young wind-sea gradually decouples from the old waves and forms a new secondary peak. Unlike the 180° wind turn, there is no decoupling in the 90° wind turn and the entire spectrum rotates smoothly in the new direction. In both cases, the young wind-sea starts developing in the new wind direction within 10 min of the wind turn for the ST6 while the directional response of the default physics lags behind with a response time that is nearly double of ST6. The modelling results highlight the differences in source term balance among the different models in SWAN. During high wind speeds, the default settings provide a larger contribution from the bottom-friction dissipation than the whitecapping. In contrast, the whitecapping

  5. Changes in the spectral pattern of selenium accumulation in Coleus blumei and the effects of chelation.

    PubMed

    Hu, Miaohao H; Yuan, Juhong H

    2015-04-01

    Chemically enhanced phytoremediation has been proposed as an effective approach to remove heavy metals from contaminated soil through the use of high biomass production plants. This study investigated changes in the spectral pattern of selenium (Se) accumulation in Coleus blumei Benth. (coleus) plants grown in hydroponics with 1.0 mg/l sodium selenite (Na2SeO3) and the effects of (S,S)-ethylenediamine disuccinic acid (EDDS) thereon through X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDXS) and Fourier transform infrared (FTIR) spectroscopy analyses. When EDDS concentrations were in the range of 0-1.0 mmol/l, Se content increased significantly; however, at EDDS concentrations above this range, the symptoms of Se toxicity were alleviated in coleus leaves. Application of EDDS over 1.0 mmol/l significantly decreased total Se uptake in the leaves and roots of the plants. The powder diffraction patterns of the roots and leaves displayed sharp crystalline peaks, which were characteristic of an organic molecule with crystallinity. Our results revealed the presence of high amounts of C, O, Mg, Al, Si, K and Ca in the roots and leaves under Se-induced stress with different concentrations of EDDS. There were no changes in the chemical compositions of the roots and leaves, but the contents were influenced by Se-induced stress and EDDS treatment. This study demonstrated the importance of applying XRD, EDXS and FTIR methods toward a more comprehensive understanding of the mechanisms of EDDS-induced Se accumulation in plants.

  6. Spatial-temporal patterns of electrocorticographic spectral changes during midazolam sedation

    PubMed Central

    Nishida, Masaaki; Zestos, Maria M.; Asano, Eishi

    2015-01-01

    Objective To better understand ‘when’ and ‘where’ wideband electrophysiological signals are altered by sedation. Methods We generated animation movies showing electrocorticography (ECoG) amplitudes at eight spectral frequency bands across 1.0 to 116 Hz, every 0.1 second, on three-dimensional surface images of 10 children who underwent epilepsy surgery. We measured the onset, intensity, and variance of each band amplitude change at given nonepileptic regions separately from those at affected regions. We also determined the presence of differential ECoG changes depending on the brain anatomy. Results Within 20 seconds following injection of midazolam, beta (16–31.5 Hz) and sigma (12–15.5 Hz) activities began to be multifocally augmented with increased variance in amplitude at each site. Beta-sigma augmentation was most prominent within the association neocortex. Augmentation of low-delta activity (1.0–1.5 Hz) was relatively modest and confined to the somatosensory-motor region. Conversely, injection of midazolam induced attenuation of theta (4.0–7.5 Hz) and high-gamma (64–116 Hz) activities. Conclusions Our observations support the notion that augmentation beta-sigma and delta activities reflects cortical deactivation or inactivation, whereas theta and high-gamma activities contribute to maintenance of consciousness. The effects of midazolam on the dynamics of cortical oscillations differed across regions. Significance Sedation, at least partially, reflects a multi-local phenomenon at the cortical level rather than global brain alteration homogeneously driven by the common central control structure. PMID:26613652

  7. Mapping and monitoring changes in vegetation communities of Jasper Ridge, CA, using spectral fractions derived from AVIRIS images

    NASA Technical Reports Server (NTRS)

    Sabol, Donald E., Jr.; Roberts, Dar A.; Adams, John B.; Smith, Milton O.

    1993-01-01

    An important application of remote sensing is to map and monitor changes over large areas of the land surface. This is particularly significant with the current interest in monitoring vegetation communities. Most of traditional methods for mapping different types of plant communities are based upon statistical classification techniques (i.e., parallel piped, nearest-neighbor, etc.) applied to uncalibrated multispectral data. Classes from these techniques are typically difficult to interpret (particularly to a field ecologist/botanist). Also, classes derived for one image can be very different from those derived from another image of the same area, making interpretation of observed temporal changes nearly impossible. More recently, neural networks have been applied to classification. Neural network classification, based upon spectral matching, is weak in dealing with spectral mixtures (a condition prevalent in images of natural surfaces). Another approach to mapping vegetation communities is based on spectral mixture analysis, which can provide a consistent framework for image interpretation. Roberts et al. (1990) mapped vegetation using the band residuals from a simple mixing model (the same spectral endmembers applied to all image pixels). Sabol et al. (1992b) and Roberts et al. (1992) used different methods to apply the most appropriate spectral endmembers to each image pixel, thereby allowing mapping of vegetation based upon the the different endmember spectra. In this paper, we describe a new approach to classification of vegetation communities based upon the spectra fractions derived from spectral mixture analysis. This approach was applied to three 1992 AVIRIS images of Jasper Ridge, California to observe seasonal changes in surface composition.

  8. DNA and protein change in tissues probed by Kubelka-Munk spectral function

    NASA Astrophysics Data System (ADS)

    Yang, Yuanlong; Celmer, Edward J.; Koutcher, Jason A.; Alfano, Robert R.

    2000-04-01

    Normal, fibroadenoma, malignant, and adipose breast tissues were investigated using Kubelka-Munk Spectral Function (KMSF). The spectral features in KMSF were identified and compared with absorption spectra determined by transmission measurements. A specified spectral feature measured in adipose tissue was assigned to (beta) -carotene, which can be used to separate fat form other molecular components in breast tissues. The peaks of (KMF) at 260nm and 280nm were attributed to DNA and proteins. The signal amplitude over 255nm to 265nm and 275nm to 285nm were found to be different for malignant fibroadenoma, and normal tissues.

  9. Asymptotic analysis of boundary value and spectral problems in thin perforated regions with rapidly changing thickness and different limiting dimensions

    SciTech Connect

    Mel'nik, Taras A; Popov, A V

    2012-08-31

    Boundary value and spectral problems for an elliptic differential equation with rapidly oscillating coefficients in a thin perforated region with rapidly changing thickness are investigated. Descriptions of asymptotic algorithms for solutions of such problems in thin regions with different limiting dimensions are combined. For a mixed inhomogeneous boundary value problem a corrector is constructed and an asymptotic estimate in the corresponding Sobolev space is established. Asymptotic bounds for eigenvalues and eigenfunctions of the Neumann spectral problems are also found. Full asymptotic expansions for the eigenvalues and eigenfunctions are constructed under certain symmetry assumptions about the structure of the thin perforated region and the coefficients of the equations. Bibliography: 21 titles.

  10. [Change of LAI and spectral response for rice under flood and waterlogging stress].

    PubMed

    Xu, Peng; Gu, Xiao-He; Meng, Lu-Min; Qiu, He; Wang, Hui-Fang

    2013-12-01

    In order to provide the foundational theoretical support for flood loss estimation of rice with RS, the change of leaf area index (LAI) and canopy spectral response during four developmental stages and three waterlogging depths were studied, and the LAI estimation model was established with spectra characteristics parameter using regression analysis method. The results show that LAI value decreases as water depth increases in tillering, jointing and heading stages, and LAI value under complete submergence decreased by 36. 36% than CK in jointing stages. "Double-Peak" presented in the canopy first derivative spectra of 680-760 nm where the red edge parameters existed, and the main peak is located in the 724-737 nm with 701 and 718 nm exhibiting secondary peak. With water depth increasing, "Triple-Peak" emerges especially. The red edge position moves to long-wavelength direction in each developmental stage. Blue shift of red edge amplitude and red edge area was detected in tillering, jointing and filling stages, while red shift appeared in heading stage. The relationship between spectra characteristics parameters and LAI were investigated during 4 growth stages, results were not consistently significant at any wavelengths, and the leaf area indices were significantly correlative to the spectra parameters before heading stage, so the spectra parameters before heading stage can be used to estimate the leaf area indices, and a regression model based on parameter D(lambda737)/D(lambda718) was recommended. Therefore the variation range of LAI for rice could response to the stress intensity directly, and the regression model LAI= 3. 138(D(lambda737)/D(lambda718))-0. 806 can precisely estimate the leaf area index under flooding and waterlogging stress.

  11. Age-Related Changes to Spectral Voice Characteristics Affect Judgments of Prosodic, Segmental, and Talker Attributes for Child and Adult Speech

    ERIC Educational Resources Information Center

    Dilley, Laura C.; Wieland, Elizabeth A.; Gamache, Jessica L.; McAuley, J. Devin; Redford, Melissa A.

    2013-01-01

    Purpose: As children mature, changes in voice spectral characteristics co-vary with changes in speech, language, and behavior. In this study, spectral characteristics were manipulated to alter the perceived ages of talkers' voices while leaving critical acoustic-prosodic correlates intact, to determine whether perceived age differences were…

  12. Measuring near infrared spectral reflectance changes from water stressed conifer stands with AIS-2

    NASA Technical Reports Server (NTRS)

    Riggs, George; Running, Steven W.

    1987-01-01

    Airborne Imaging Spectrometer-2 (AIS-2) data was acquired over two paired conifer stands for the purpose of detecting differences in spectral reflectance between stressed and natural canopies. Water stress was induced in a stand of Norway spruce and white pine by severing the sapwood near the ground. Water stress during the AIS flights was evaluated through shoot water potential and relative water content measurements. Preliminary analysis with raw AIS-2 data using SPAM indicates that there were small, inconsistent differences in absolute spectral reflectance in the near infrared 0.97 to 1.3 micron between the stressed and natural canopies.

  13. Photoinduced heterostructure in a vanadium dioxide film

    NASA Astrophysics Data System (ADS)

    Semenov, A. L.

    2017-02-01

    A photoinduced semiconductor-metal phase transition that occurs in a surface layer of vanadium dioxide film on an aluminum substrate within the time Δ t < 1 ps has been studied theoretically. A nonthermal mechanism of the development of instability has been considered. It has been shown that a heterophase structure containing metallic and semiconductor layers is formed in the VO2 film. The phase transition time τ has been calculated as a function of the distance z from the film surface. Comparison with the experiment has been carried out.

  14. Spectral changes in conifers subjected to air pollution and water stress: Experimental studies

    NASA Technical Reports Server (NTRS)

    Westman, Walter E.; Price, Curtis V.

    1988-01-01

    The roles of leaf anatomy, moisture and pigment content, and number of leaf layers on spectral reflectance in healthy, pollution-stressed, and water-stressed conifer needles were examined experimentally. Jeffrey pine (Pinus jeffreyi) and giant sequoia (Sequoiadendron gigantea) were exposed to ozone and acid mist treatments in fumigation chambers; red pine (Pinus resinosa) needles were artificially dried. Infrared reflectance from stacked needles rose with free water loss. In an air-drying experiment, cell volume reductions induced by loss of turgor caused near-infrared reflectance (TM band 4) to drop after most free water was lost. Under acid mist fumigation, stunting of tissue development similarly reduced band 4 reflectance. Both artificial drying and pollutant fumigation caused a blue shift of the red edge of spectral reflectance curves in conifers, attributable to chlorophyll denaturation. Thematic mapper band ratio 4/3 fell and 5/4 rose with increasing pollution stress on artificial drying. Loss of water by air-drying, freeze-drying, or oven-drying enhanced spectral features, due in part to greater scattering and reduced water absorption. Grinding of the leaf tissue further enhanced the spectral features by increasing reflecting surfaces and path length. In a leaf-stacking experiment, an asymptote in visible and infrared reflectance was reached at 7-8 needle layers of red pine.

  15. Change in Drusen Area Over Time Compared Using Spectral-Domain Optical Coherence Tomography and Color Fundus Imaging

    PubMed Central

    Gregori, Giovanni; Yehoshua, Zohar; Garcia Filho, Carlos Alexandre de Amorim; Sadda, SriniVas R.; Portella Nunes, Renata; Feuer, William J.; Rosenfeld, Philip J.

    2014-01-01

    Purpose. To investigate the relationship between drusen areas measured with color fundus images (CFIs) and those with spectral-domain optical coherence tomography (SDOCT). Methods. Forty-two eyes from thirty patients with drusen in the absence of geographic atrophy were recruited to a prospective study. Digital color fundus images and SDOCT images were obtained at baseline and at follow-up visits at 3 and 6 months. Registered, matched circles centered on the fovea with diameters of 3 mm and 5 mm were identified on both CFIs and SDOCT images. Spectral-domain OCT drusen measurements were obtained using a commercially available proprietary algorithm. Drusen boundaries on CFIs were traced manually at the Doheny Eye Institute Image Reading Center. Results. Mean square root drusen area (SQDA) measurements for the 3-mm circles on the SDOCT images were 1.451 mm at baseline and 1.464 mm at week 26, whereas the measurements on CFIs were 1.555 mm at baseline and 1.584 mm at week 26. Mean SQDA measurements from CFIs were larger than those from the SDOCT measurements at all time points (P = 0.004 at baseline, P = 0.003 at 26 weeks). Changes in SQDA over 26 weeks measured with SDOCT were not different from those measured with CFIs (mean difference = 0.014 mm, P = 0.5). Conclusions. Spectral-domain OCT drusen area measurements were smaller than the measurements obtained from CFIs. However, there were no differences in the change in drusen area over time between the two imaging modalities. Spectral-domain OCT measurements were considerably more sensitive in assessing drusen area changes. PMID:25335982

  16. Photoinduced Force Mapping of Plasmonic Nanostructures.

    PubMed

    Tumkur, Thejaswi U; Yang, Xiao; Cerjan, Benjamin; Halas, Naomi J; Nordlander, Peter; Thomann, Isabell

    2016-12-14

    The ability to image the optical near-fields of nanoscale structures, map their morphology, and concurrently obtain spectroscopic information, all with high spatiotemporal resolution, is a highly sought-after technique in nanophotonics. As a step toward this goal, we demonstrate the mapping of electromagnetic forces between a nanoscale tip and an optically excited sample consisting of plasmonic nanostructures with an imaging platform based on atomic force microscopy. We present the first detailed joint experimental-theoretical study of this type of photoinduced force microscopy. We show that the enhancement of near-field optical forces in gold disk dimers and nanorods follows the expected plasmonic field enhancements with strong polarization sensitivity. We then introduce a new way to evaluate optically induced tip-sample forces by simulating realistic geometries of the tip and sample. We decompose the calculated forces into in-plane and out-of-plane components and compare the calculated and measured force enhancements in the fabricated plasmonic structures. Finally, we show the usefulness of photoinduced force mapping for characterizing the heterogeneity of near-field enhancements in precisely e-beam fabricated nominally alike nanostructures - a capability of widespread interest for precise nanomanufacturing, SERS, and photocatalysis applications.

  17. Nanoscale chemical imaging by photoinduced force microscopy

    PubMed Central

    Nowak, Derek; Morrison, William; Wickramasinghe, H. Kumar; Jahng, Junghoon; Potma, Eric; Wan, Lei; Ruiz, Ricardo; Albrecht, Thomas R.; Schmidt, Kristin; Frommer, Jane; Sanders, Daniel P.; Park, Sung

    2016-01-01

    Correlating spatial chemical information with the morphology of closely packed nanostructures remains a challenge for the scientific community. For example, supramolecular self-assembly, which provides a powerful and low-cost way to create nanoscale patterns and engineered nanostructures, is not easily interrogated in real space via existing nondestructive techniques based on optics or electrons. A novel scanning probe technique called infrared photoinduced force microscopy (IR PiFM) directly measures the photoinduced polarizability of the sample in the near field by detecting the time-integrated force between the tip and the sample. By imaging at multiple IR wavelengths corresponding to absorption peaks of different chemical species, PiFM has demonstrated the ability to spatially map nm-scale patterns of the individual chemical components of two different types of self-assembled block copolymer films. With chemical-specific nanometer-scale imaging, PiFM provides a powerful new analytical method for deepening our understanding of nanomaterials. PMID:27051870

  18. On-Line Change Monitoring with Transformed Multi-Spectral Time Series, a Study Case in Tropical Forest

    NASA Astrophysics Data System (ADS)

    Lu, Meng; Hamunyela, Eliakim

    2016-10-01

    In recent years, the methods for detecting structural changes in time series have been adapted for forest disturbance monitoring using satellite data. The BFAST (Breaks For Additive Season and Trend) Monitor framework, which detects forest cover disturbances from satellite image time series based on empirical fluctuation tests, is particularly used for near real-time deforestation monitoring, and it has been shown to be robust in detecting forest disturbances. Typically, a vegetation index that is transformed from spectral bands into feature space (e.g. normalised difference vegetation index (NDVI)) is used as input for BFAST Monitor. However, using a vegetation index for deforestation monitoring is a major limitation because it is difficult to separate deforestation from multiple seasonality effects, noise, and other forest disturbance. In this study, we address such limitation by exploiting the multi-spectral band of satellite data. To demonstrate our approach, we carried out a case study in a deciduous tropical forest in Bolivia, South America. We reduce the dimensionality from spectral bands, space and time with projective methods particularly the Principal Component Analysis (PCA), resulting in a new index that is more suitable for change monitoring. Our results show significantly improved temporal delay in deforestation detection. With our approach, we achieved a median temporal lag of 6 observations, which was significantly shorter than the temporal lags from conventional approaches (14 to 21 observations).

  19. In situ optical measurements of Chang'E-3 landing site in Mare Imbrium: 1. Mineral abundances inferred from spectral reflectance

    NASA Astrophysics Data System (ADS)

    Zhang, Hao; Yang, Yazhou; Yuan, Ye; Jin, Weidong; Lucey, Paul G.; Zhu, Meng-Hua; Kaydash, Vadim G.; Shkuratov, Yuriy G.; Di, Kaichang; Wan, Wenhui; Xu, Bin; Xiao, Long; Wang, Ziwei; Xue, Bin

    2015-09-01

    The visible and near-infrared imaging spectrometer on board the Yutu Rover of Chinese Chang'E-3 mission measured the lunar surface reflectance at a close distance (~1 m) and collected four spectra at four different sites. These in situ lunar spectra have revealed less mature features than that measured remotely by spaceborne sensors such as the Moon Mineralogy Mapper instrument on board the Chandrayaan-1 mission and the Spectral Profiler on board the Kaguya over the same region. Mineral composition analysis using a spectral lookup table populated with a radiative transfer mixing model has shown that the regolith at the landing site contains high abundance of olivine. The mineral abundance results are consistent with that inferred from the compound measurement made by the on board alpha-particle X-ray spectrometer.

  20. Time-resolved x-ray absorption spectroscopy of photoinduced insulator-metal transition in a colossal magnetoresistive manganite

    SciTech Connect

    Rini, M.; Tobey, R.; Wall, S.; Zhu, Y.; Tomioka, Y.; Tokura, Y.; Cavalleri, A.; Schoenlein, R.W.

    2008-08-01

    We studied the ultrafast insulator-metal transition in a manganite by means of picosecond X-ray absorption at the O K- and Mn L-edges, probing photoinduced changes in O-2p and Mn-3d electronic states near the Fermi level.

  1. DNA and protein changes caused by disease in human breast tissues probed by the Kubelka-Munk spectral functional.

    PubMed

    Yang, Yuanlong; Celmer, Edward J; Koutcher, Jason A; Alfano, R R

    2002-06-01

    Malignant, fibroadenoma, normal and adipose breast tissues were studied using diffuse reflectance spectroscopy. The absorption spectra of the breast tissues were extracted from the diffuse reflectance spectra using the Kubelka-Munk function (K-M function). The spectral features of the K-M function were identified and compared with those of the absorption spectra. The spectral features of the K-M function were assigned to DNA, protein, beta-carotene and hemoglobin (oxygenated and deoxygenated) molecules in the breast tissue. The amplitudes of the K-M function averaged from 275 to 285 nm and from 255 to 265 nm and were found to be different for malignant, fibroadenoma and normal tissues. These differences were attributed to changes in proteins and DNA. A set of critical parameters was determined for separating malignant tissues from fibroadenoma and normal tissues. This approach should hold for other tissue types such as cervix, uterus and colon.

  2. Effect of topographic correction on forest change detection using spectral trend analysis of Landsat pixel-based composites

    NASA Astrophysics Data System (ADS)

    Chance, Curtis M.; Hermosilla, Txomin; Coops, Nicholas C.; Wulder, Michael A.; White, Joanne C.

    2016-02-01

    Pixel-based image compositing enables production of large-area surface reflectance images that are largely devoid of clouds, cloud shadows, or haze. Change detection with spectral trend analysis uses a dense time series of images, such as pixel-based composites, to quantify the year, amount, and magnitude of landscape changes. Topographically-related shadows found in mountainous terrain may confound trend-based forest change detection approaches. In this study, we evaluate the impact of topographic correction on trend-based forest change detection outcomes by comparing the amount and location of changes identified on an image composite with and without a topographic correction. Moreover, we evaluated two different approaches to topographic correction that are relevant to pixel-based image composites: the first corrects each pixel according to the day of year (DOY) the pixel was acquired, whilst the second corrects all pixels to a single reference date (August 1st), which was also the target date for generating the pixel-based image composite. Our results indicate that a greater area of change is detected when no topographic correction is applied to the image composite, however, the difference in change area detected between no correction and either the DOY or the August 1st correction is minor and less than 1% (0.54-0.85%). The spatial correspondence of these different approaches is 96.2% for the DOY correction and 97.7% for the August 1st correction. The largest differences between the correction processes occur in valleys (0.71-1.14%), upper slopes (0.71-1.09%), and ridges (0.73-1.09%). While additional tests under different conditions and in other environments are encouraged, our results indicate that topographic correction may not be justified in change detection routines computing spectral trends from pixel-based composites.

  3. Aluminum-induced changes in properties and fouling propensity of DOM solutions revealed by UV-vis absorbance spectral parameters.

    PubMed

    Zhou, Minghao; Meng, Fangang

    2016-04-15

    The integration of pre-coagulation with ultrafiltration (UF) is expected to not only reduce membrane fouling but also improve natural organic matter (NOM) removal. However, it is difficult to determine the proper coagulant dosage for different water qualities. The objective of this study was to probe the potential of UV-vis spectroscopic analysis to reveal the coagulant-induced changes in the fouling potentials of dissolved organic matter (DOM) and to determine the optimal coagulant dosage. The Zeta potentials (ZPs) and average particle size of the four DOM solutions (Aldrich humic acid (AHA), AHA-sodium alginate (SA), AHA-bovine serum albumin (BSA) and AHA-dextran (DEX)) coagulated with aluminum chloride (AlCl3) were measured. Results showed that increasing the aluminum coagulant dosage induced the aggregation of DOM. Meanwhile, the addition of aluminum coagulant resulted in an increase in DSlope(325-375) (the slope of the log-transformed absorbance spectra from 325 to 375 nm) and a decrease in S(275-295) (the slope of the log-transformed absorption coefficient from 275 to 295 nm) and SR (the ratio of Slope(275-295) and Slope(350-400)). The variations of these spectral parameters (i.e., DSlope(325-375), S(275-295) and SR) correlated well with the aluminum-caused changes in ZPs and average particle size. This implies that spectral parameters have the potential to indicate DOM aggregation. In addition, good correlations of spectral parameters and membrane fouling behaviors (i.e., unified membrane fouling index (UMFI)) suggest that the changes in DSlope(325-375), S(275-295) and SR were indicative of the aluminum-caused alterations of fouling potentials of all DOM solutions. Interestingly, the optimal dosage of aluminum (40 μM for AHA, AHA-BSA, and AHA-DEX) was obtained based on the relation between spectral parameters and fouling behaviors. Overall, the spectroscopic analysis, particularly for the utilization of spectral parameters, provided a convenient approach

  4. The photoinduced dynamics of X[M(dmit)2]2 salts

    NASA Astrophysics Data System (ADS)

    Ishikawa, Tadahiko; Hayes, Stuart A.; Miller, R. J. Dwayne; Hada, Masaki; Koshihara, Shinya

    2017-03-01

    We review our work on the photoinduced dynamics of X[M(dmit)2]2 salts in the charge-separated (CS) phase from the viewpoints of both electronic structural change and lattice or molecular structural change. The driving force for the CS phase formation is a strong correlation among the charge distribution, orbital energies, and the molecular structure; this is in contrast to frequently studied charge-ordered systems such as EDOTTF2PF6, whose formation is mainly driven by the intersite Coulomb repulsion. Despite the localized nature of the structural component, the cooperativity inherent to the crystal is likely to play an important role in photoinduced phenomena. In this review, we summarize the results obtained by a series of optical pump-probe experiments on this class of materials. We have also recently extended these studies using ultrafast electron diffraction to follow the nuclear motion in one of these systems. Such information is crucial for a full understanding of the photoinduced phenomena and it is anticipated that combining the results of the optical and diffraction studies will lead to more fruitful insight than either technique can offer in isolation.

  5. Origin of photo-induced transmitting oscillations in chalcogenide glasses.

    PubMed

    Tao, HaiZheng; Yang, ZhiYong; Lucas, Pierre

    2009-09-28

    Light-induced oscillatory behaviors of transmission in chalcogenide glasses are investigated using a continuous wave tunable Ti-sapphire laser. It is shown that phase change, thermal fluctuation, nonlinear index change and periodic self focusing are not at the origin of light-induced oscillatory transmittance in chalcogenide glasses. Instead, results indicate that the interference of transmitting and reflecting light is at the origin of the oscillatory behaviors of transmitted light. Just like the principle of Fabry-Pérot interferometer, these interferences result in a periodic change in transmission as the related interferential beams get in and out of phase. However, this transmitting oscillatory behavior can be registered by the detector only when the change of optical path length difference initiated by photo-induced effects is slower enough compared with the corresponding response time of the detector. Several photo-structural effects contribute to that phenomenon including photo-expansion, photo-darkening, and permanent self focusing. It appears that fluctuations of the light source intensity induce a wide distribution of the oscillatory periods.

  6. Change Analysis of the Spectral Characteristics of Rubber Trees at Canopy and Leaf Scales during the Brazilian Autumn

    NASA Astrophysics Data System (ADS)

    Amaral, C. H.; Almeida, T. I. R.; Quitério, G. C. M.; Alves, M. N.; Souza Filho, C. R.

    2012-07-01

    The objective of this work is to investigate the hyperspectral remote sensing potential to detect spectral changes undergone by clones of two rubber trees within Brazilian Autumn, with decrease of rain, temperature and photoperiod between May and June. Indirectly, we also analyze the ability of the data to help discriminating the clones at two dates in autumn. The average canopy spectra of the stands were obtained with two overpasses of the ProSpecTIR-VS airborne hyperspectral sensor (357 bands between 400-2,500 nm; spatial resolution of 1m) by 14th May and 17th June, in 2010 year. Additionally measurements of leaf spectra were taken in the same dates, but in the 2011 year. Considering the analysis of the spectra measured from the three stands, this indicates that spectral differences in the VIS (400-700 nm) region are of genetic origin and occur regardless of environmental conditions and period of data collection. In the NIR (700-1,300 nm) range, the environmental factors predominate in the two periods of data collection. The SWIR (1,300-2,500 nm) displayed the largest differences between the months of data collection. In May, the relationship between stands indicated the prevalence of environmental aspects. However, in June, the stands and clones spectral behaviour indicates that as the temperature, the rainfall and the photoperiod are lower closer to winter, the SWIR can be effectively used to discriminate and map these clones separately.

  7. Absolute Power Spectral Density Changes in the Magnetoencephalographic Activity During the Transition from Childhood to Adulthood.

    PubMed

    Gómez, Carlos M; Rodríguez-Martínez, Elena I; Fernández, Alberto; Maestú, Fernando; Poza, Jesús; Gómez, Carlos

    2017-01-01

    The aim of this study was to define the pattern of reduction in absolute power spectral density (PSD) of magnetoencephalography (MEG) signals throughout development. Specifically, we wanted to explore whether the human skull's high permeability for electromagnetic fields would allow us to question whether the pattern of absolute PSD reduction observed in the human electroencephalogram is due to an increase in the skull's resistive properties with age. Furthermore, the topography of the MEG signals during maturation was explored, providing additional insights about the areas and brain rhythms related to late maturation in the human brain. To attain these goals, spontaneous MEG activity was recorded from 148 sensors in a sample of 59 subjects divided into three age groups: children/adolescents (7-14 years), young adults (17-20 years) and adults (21-26 years). Statistical testing was carried out by means of an analysis of variance (ANOVA), with "age group" as between-subject factor and "sensor group" as within-subject factor. Additionally, correlations of absolute PSD with age were computed to assess the influence of age on the spectral content of MEG signals. Results showed a broadband PSD decrease in frontal areas, which suggests the late maturation of this region, but also a mild increase in high frequency PSD with age in posterior areas. These findings suggest that the intensity of the neural sources during spontaneous brain activity decreases with age, which may be related to synaptic pruning.

  8. Photo-induced electron transfer method

    DOEpatents

    Wohlgemuth, R.; Calvin, M.

    1984-01-24

    The efficiency of photo-induced electron transfer reactions is increased and the back transfer of electrons in such reactions is greatly reduced when a photo-sensitizer zinc porphyrin-surfactant and an electron donor manganese porphyrin-surfactant are admixed into phospholipid membranes. The phospholipids comprising said membranes are selected from phospholipids whose head portions are negatively charged. Said membranes are contacted with an aqueous medium in which an essentially neutral viologen electron acceptor is admixed. Catalysts capable of transferring electrons from reduced viologen electron acceptor to hydrogen to produce elemental hydrogen are also included in the aqueous medium. An oxidizable olefin is also admixed in the phospholipid for the purpose of combining with oxygen that coordinates with oxidized electron donor manganese porphyrin-surfactant.

  9. Photo-induced electron transfer method

    DOEpatents

    Wohlgemuth, Roland; Calvin, Melvin

    1984-01-01

    The efficiency of photo-induced electron transfer reactions is increased and the back transfer of electrons in such reactions is greatly reduced when a photo-sensitizer zinc porphyrin-surfactant and an electron donor manganese porphyrin-surfactant are admixed into phospho-lipid membranes. The phospholipids comprising said membranes are selected from phospholipids whose head portions are negatively charged. Said membranes are contacted with an aqueous medium in which an essentially neutral viologen electron acceptor is admixed. Catalysts capable of transfering electrons from reduced viologen electron acceptor to hydrogen to produce elemental hydrogen are also included in the aqueous medium. An oxidizable olefin is also admixed in the phospholipid for the purpose of combining with oxygen that coordinates with oxidized electron donor manganese porphyrin-surfactant.

  10. Photoinduced decomposition of trichloroethylene in soil components

    SciTech Connect

    Tao, T.; Yang, J.J.; Maciel, G.E.

    1999-01-01

    The photoinduced decomposition of trichloroethylene adsorbed on Ca-montmorillonite by long-wavelength UV irradiation has been studied in a quartz tube open to air or through which air or oxygen is passed. Solid-sample and liquid-solution NMR techniques were used to identify apparent products or intermediates of the photodecomposition. Dichloroacetic acid was identified as a major organic product/intermediate; substantial amounts of pentachloroethane and trichloroacetic acid were also identified. The formation of CO{sub 2} was characterized quantitatively by wet chemical analysis. About 40% and 57%, respectively, of the total carbon of trichloroethylene was converted to carbon dioxide in air and O{sub 2} environments over a period of 16 days. Phosgene and HCl were also detected. The photodecomposition of trichloroethylene adsorbed on whole soil, on Zn{sup 2+}-exchanged and Cu{sup 2+}-exchanged montmorillonites, on kaolinite, and on silica gel was also examined in less detail; qualitatively, the conversion of trichloroethylene to dichloroacetic acid in a 48-h period occurred with the following order of decreasing efficiencies: Zn{sup 2+}-montmorillonite > silica gel > kaolinite > Ca{sup 2+}-montmorillonite > whole soil > Cu{sup 2+}-montmorillonite. These results show that the photoinduced decomposition of adsorbed trichloroethylene occurs on a variety of adsorbents, generating products and intermediates that are similar to what have been reported previously for TiO{sub 2}-based photodecomposition but with much longer time scales. These conversions can, therefore, be expected to occur in sunlight at the air-soil interface.

  11. Absorption spectral change of peripheral-light harvesting complexes 2 induced by magnesium protoporphyrin IX monomethyl ester association

    NASA Astrophysics Data System (ADS)

    Yue, Huiying; Zhao, Chungui; Li, Kai; Yang, Suping

    2015-02-01

    Several spectrally different types of peripheral light harvesting complexes (LH) have been reported in anoxygenic phototrophic bacteria in response to environmental changes. In this study, two spectral forms of LH2 (T-LH2 and U-LH2) were isolated from Rhodobacter azotoformans. The absorption of T-LH2 was extremely similar to the LH2 isolated from Rhodobacter sphaeroides. U-LH2 showed an extra peak at ∼423 nm in the carotenoid region. To explore the spectral origin of this absorption peak, the difference in pigment compositions of two LH2 was analyzed. Spheroidene and bacteriochlorophyll aP were both contained in the two LH2. And magnesium protoporphyrin IX monomethyl ester (MPE) was only contained in U-LH2. It is known that spheroidene and bacteriochlorophyll aP do not produce ∼423 nm absorption peak either in vivo or in vitro. Whether MPE accumulation was mainly responsible for the formation of the ∼423 nm peak? The interactions between MPE and different proteins were further studied. The results showed that the maximum absorption of MPE was red-shifted from ∼415 nm to ∼423 nm when it was mixed with T-LH2 and its apoproteins, nevertheless, the Qy transitions of the bound bacteriochlorophylls in LH2 were almost unaffected, which indicated that the formation of the ∼423 nm peak was related to MPE-LH2 protein interaction. MPE did not bind to sites involved in the spectral tuning of BChls, but the conformation of integral LH2 was affected by MPE association, the alkaline stability of U-LH2 was lower than T-LH2, and the fluorescence intensity at 860 nm was decreased after MPE combination.

  12. Review of the photo-induced toxicity of environmental contaminants.

    PubMed

    Roberts, Aaron P; Alloy, Matthew M; Oris, James T

    2017-01-01

    Solar radiation is a vital component of ecosystem function. However, sunlight can also interact with certain xenobiotic compounds in a phenomenon known as photo-induced, photo-enhanced, photo-activated, or photo-toxicity. This phenomenon broadly refers to an interaction between a chemical and sunlight resulting in increased toxicity. Because most aquatic ecosystems receive some amount of sunlight, co-exposure to xenobiotic chemicals and solar radiation is likely to occur in the environment, and photo-induced toxicity may be an important factor impacting aquatic ecosystems. However, photo-induced toxicity is not likely to be relevant in all aquatic systems or exposure scenarios due to variation in important ecological factors as well as physiological adaptations of the species that reside there. Here, we provide an updated review of the state of the science of photo-induced toxicity in aquatic ecosystems.

  13. Spectral analysis of skeletal muscle changes resulting from 59 days of weightlessness in Skylab 2

    NASA Technical Reports Server (NTRS)

    Lafevers, E. V.; Nicogossian, A. E.; Hoffler, G. W.; Hursta, W.; Baker, J.

    1975-01-01

    During stressful exercise of the m. gastrocnemius, preflight and postflight surface electromyograms (EMG) were taken from each of the Skylab II astronauts. Measurements on the muscle were made once 5 days before launch, and four times postflight on recovery day, 4 days after recovery, 16 days after recovery and 29 days after recovery. It was hypothesized that the disused gastrocnemius would exhibit dysfunction characteristics similar to those found in laboratory studies on disuse and of pathologically astrophied muscle, and that physical stress would be associated with heightened fatigability in the muscle. Both hypotheses were sustained. The results showed significant shifts of the predominant frequency of the gastrocnemius into higher than normal bands which suggests a relationship between muscle disuse characteristics and pathologic dysfunction characteristics. It was concluded that the spectrally analyzed EMG is a sensitive measure of muscle dsyfunction that is associated with disuse. Antigravity muscles exhibit heightened susceptibility to fatigue when subjected to lengthy weightlessness.

  14. Photoinduced nanocomposites—creation, modification, linear and nonlinear optical properties

    NASA Astrophysics Data System (ADS)

    Bityurin, N.; Alexandrov, A.; Afanasiev, A.; Agareva, N.; Pikulin, A.; Sapogova, N.; Soustov, L.; Salomatina, E.; Gorshkova, E.; Tsverova, N.; Smirnova, L.

    2013-07-01

    UV irradiation of materials consisting of a polymer matrix that possesses precursors of noble metals followed by annealing results in creation of metal nanoparticles within the irradiated domains. Such photoinduced nanocomposites are promising for photonics applications due to the strong alteration of their optical properties compared to initial nonirradiated materials. We report our results on the synthesis and investigation of two kinds of these materials: (a) Photoinduced Au nanocomposites based on PMMA matrices, including bulk materials prepared by means of the polymerization technique;

  15. Capturing ultrafast photoinduced local structural distortion of BiFeO3

    SciTech Connect

    Wen, Haidan; Sassi, Michel; Luo, Zhenlin; Adamo, Carolina; Schlom, Darrell G.; Rosso, Kevin M.; Zhang, Xiaoyi

    2015-10-14

    The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3 film. The out-of-plane elongation of the unit cell is accompanied by the in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This anisotropic elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated non-equilibrium processes in polar materials.

  16. Capturing ultrafast photoinduced local structural distortions of BiFeO3

    SciTech Connect

    Wen, Haidan; Sassi, Michel JPC; Luo, Zhenlin; Adamo, Carolina; Schlom, Darrell; Rosso, Kevin M.; Zhang, Xiaoyi

    2015-10-14

    The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3 film. The out-of-plane elongation of the unit cell is accompanied by the in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This uniaxial elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated nonequilibrium processes in polar materials.

  17. Capturing ultrafast photoinduced local structural distortions of BiFeO3

    DOE PAGES

    Wen, Haidan; Sassi, Michel JPC; Luo, Zhenlin; ...

    2015-10-14

    The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3 film. The out-of-plane elongation of the unit cell is accompanied by themore » in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This uniaxial elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated nonequilibrium processes in polar materials.« less

  18. Capturing ultrafast photoinduced local structural distortions of BiFeO3

    NASA Astrophysics Data System (ADS)

    Wen, Haidan; Sassi, Michel; Luo, Zhenlin; Adamo, Carolina; Schlom, Darrell G.; Rosso, Kevin M.; Zhang, Xiaoyi

    2015-10-01

    The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3 film. The out-of-plane elongation of the unit cell is accompanied by the in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This anisotropic elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated non-equilibrium processes in polar materials.

  19. The nature of photoinduced phase transition and metastable states in vanadium dioxide

    PubMed Central

    Tao, Zhensheng; Zhou, Faran; Han, Tzong-Ru T.; Torres, David; Wang, Tongyu; Sepulveda, Nelson; Chang, Kiseok; Young, Margaret; Lunt, Richard R.; Ruan, Chong-Yu

    2016-01-01

    Photoinduced threshold switching processes that lead to bistability and the formation of metastable phases in photoinduced phase transition of VO2 are elucidated through ultrafast electron diffraction and diffusive scattering techniques with varying excitation wavelengths. We uncover two distinct regimes of the dynamical phase change: a nearly instantaneous crossover into an intermediate state and its decay led by lattice instabilities over 10 ps timescales. The structure of this intermediate state is identified to be monoclinic, but more akin to M2 rather than M1 based on structure refinements. The extinction of all major monoclinic features within just a few picoseconds at the above-threshold-level (~20%) photoexcitations and the distinct dynamics in diffusive scattering that represents medium-range atomic fluctuations at two photon wavelengths strongly suggest a density-driven and nonthermal pathway for the initial process of the photoinduced phase transition. These results highlight the critical roles of electron correlations and lattice instabilities in driving and controlling phase transformations far from equilibrium. PMID:27982066

  20. The nature of photoinduced phase transition and metastable states in vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Tao, Zhensheng; Zhou, Faran; Han, Tzong-Ru T.; Torres, David; Wang, Tongyu; Sepulveda, Nelson; Chang, Kiseok; Young, Margaret; Lunt, Richard R.; Ruan, Chong-Yu

    2016-12-01

    Photoinduced threshold switching processes that lead to bistability and the formation of metastable phases in photoinduced phase transition of VO2 are elucidated through ultrafast electron diffraction and diffusive scattering techniques with varying excitation wavelengths. We uncover two distinct regimes of the dynamical phase change: a nearly instantaneous crossover into an intermediate state and its decay led by lattice instabilities over 10 ps timescales. The structure of this intermediate state is identified to be monoclinic, but more akin to M2 rather than M1 based on structure refinements. The extinction of all major monoclinic features within just a few picoseconds at the above-threshold-level (~20%) photoexcitations and the distinct dynamics in diffusive scattering that represents medium-range atomic fluctuations at two photon wavelengths strongly suggest a density-driven and nonthermal pathway for the initial process of the photoinduced phase transition. These results highlight the critical roles of electron correlations and lattice instabilities in driving and controlling phase transformations far from equilibrium.

  1. Spectral changes with the direction of asteroid impact at Lonar crater, India: Findings from Mid-IR DRIFT analysis

    NASA Astrophysics Data System (ADS)

    Basavaiah, Nathani; Shriram Chavan, Rajesh

    2013-04-01

    Meteoritic Impact Cratering is an important geologic process which is affecting all planetary bodies throughout the solar system including Earth and Mars. There are abundance of impact craters on the Earth and Mars. Identifying spectral signatures have important implications for understanding mineralogy and also geology of these craters. Fortuitously, Lonar Impact Crater in India is the only well-preserved terrestrial crater excavated completely on Deccan basalts and serves as an "excellent analogue" to craters on Mars and Moon [1]. Reported here are results of Mid-Infrared (1400-400 cm-1) spectroscopic studies on fine-grained (<45 μm) basaltic rock powers from this crater using Diffuse (Biconical) Reflectance Infrared Fourier Transform (DRIFT) technique. Spectral data of the shock metamorphism of basaltic rock powders are examined. Infrared spectra of rock powders of relatively unshocked and shocked basalts are obtained to document the mineralogical and hence spectral variations with the direction of impact and thereby distribution of primary Tectosilicate, Inosilicate(e.g. Plagioclase Feldspar, Pyroxene etc) and secondary Phyllosilicate minerals (e.g. Illite, Smectite, Saponite, Serpentine etc). The results show relative loss of spectral features in western sector compared to eastern sector as a result of increased shock wave distribution and subsequent disordering of primary mineralogy. From east (direction of impact) to western sector, spectral features of all samples change systematically. The major changes are (i) line shifts, which are more pronounced in western sector than in eastern sector and (ii) all spectra show a systematic weakening in intensity and strength, and thus resulting in only few absorption bands in western sector. Also, all the samples display drastic decrease in strength and intensity of 590 cm-1 absorption band which has been considered very sensitive to the structural changes induced by shock pressure in feldspars dominant rocks[2]and

  2. Photoinduced electron transfer reaction in polymer-surfactant aggregates: Photoinduced electron transfer between N,N-dimethylaniline and 7-amino coumarin dyes

    SciTech Connect

    Chakraborty, Anjan; Seth, Debabrata; Setua, Palash; Sarkar, Nilmoni

    2008-05-28

    Photoinduced electron transfer between coumarin dyes and N,N-dimethylaniline has been investigated by using steady state and picosecond time resolved fluorescence spectroscopy in sodium dodecyl sulphate (SDS) micelles and PVP-polyvinyl pyrrolidone (SDS) polymer-surfactant aggregates. A slower rate of electron transfer is observed in PVP-SDS aggregates than in polymer-free SDS micelles. A Marcus type inversion is observed in the correlation of free energy change in comparison with the electron transfer rate. The careful investigation reveals that C-151 deviates from the normal Marcus inverted region compared to its analogs C-152 and C-481 due to slower rotational relaxation and smaller translational diffusion coefficient.

  3. Spectral Changes of Cucumber Leaf During Adaptation of the Photosynthetic Apparatus to Led Lighting

    NASA Astrophysics Data System (ADS)

    Viazau, Y. V.; Kozel, N. V.; Domanski, V. P.; Shalygo, N. V.

    2015-01-01

    A direct correlation between the change of fluorescence at 77 K in leaves of cucumber plants growing under LED lighting and the change of the quantitative composition of structural proteins of PS1 and PS2 was established. It was shown that light absorption and the utilization of its energy during the long-term action of narrow-band light on cucumber plants could affect considerably spectra of the leaves because of changes in the synthesis of photosystem structural proteins.

  4. Convergent synthesis and photoinduced processes in multi-chromophoric rotaxanes.

    PubMed

    Megiatto, Jackson D; Li, Ke; Schuster, David I; Palkar, Amit; Herranz, M Ángeles; Echegoyen, Luis; Abwandner, Silke; de Miguel, Gustavo; Guldi, Dirk M

    2010-11-18

    A series of [2]rotaxane materials, in which [60]fullerene is linked to a macrocycle and ferrocene (Fc) moieties are placed at the termini of a thread, both of which possess a central Cu(I)-1,10-phenanthroline [Cu(phen)(2)](+) complex, were synthesized by self-assembly using Sauvage metal template methodology. Two types of threads were constructed, one with terminal ester linkages, and a second with terminal 1,2,3-triazole linkages derived from Cu(I)-catalyzed "click" 1,3-cycloaddition reactions. Model compounds lacking the fullerene moiety were prepared in an analogous manner. The ability of the interlocked Fc-[Cu(phen)(2)](+)-C(60) hybrids to undergo electron transfer upon photoexcitation in benzonitrile, dichloromethane, and ortho-dichlorobenzene was investigated by means of time-resolved fluorescence and transient absorption spectroscopy, using excitation wavelengths directed at the fullerene and [Cu(phen)(2)](+) subunits. The energies of the electronic excited states and charge separated (CS) states that might be formed upon photoexcitation were determined from spectroscopic and electrochemical data. These studies showed that MLCT excited states of the copper complex in the fullerenerotaxanes were quenched by electron transfer to the fullerene in benzonitrile, resulting in charge separated states with oxidized copper and reduced fullerene moieties, (Fc)(2)-[Cu(phen)(2)](2+)-C(60)(•-). Even though electron transfer from Fc to the oxidized copper complex is predicted to be exergonic by 0.16 to 0.20 eV, no unequivocal evidence in support of such a process was obtained. The conclusion that Fc plays no role in the photoinduced processes in our systems rests on the lack of enhancement of the lifetime of the charge separated state, as measured by decay of C(60)(•-) at ∼1000 nm, since one-electron oxidized Fc is very difficult to detect spectroscopically in the 500-800 nm spectral region.

  5. Changes in spectral reflectance of wheat leaves in response to specific macronutrient deficiency

    NASA Astrophysics Data System (ADS)

    Ayala-Silva, Tomas; Beyl, Caula A.

    In wheat (Triticum aestivum L.) plants, deficiency of an essential element may drastically affect growth, appearance, and most importantly yield. Wheat, the focus of this study, is one of the crops studied in the CELSS program. Information about nutrient deficiencies in crops grown in controlled environment is essential to optimize food productivity. The main objective of this study was to determine whether deficiency of Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca) and Magnesium (M) alters spectral reflectance properties of wheat leaves. Plants were grown in the greenhouse and growth chamber, in a modified Hoagland’s nutrient solution. Spectral reflectance of fully expanded wheat leaves from 280 to 1100 nm, nutrient concentrations (N, P, K, and Ca) and chlorophyll (Chl) were determined when deficiency symptoms were first evident (≈6 7 weeks). Chlorophyll content and fresh and dry weight, were used to assess the severity of the nutrient stress. All nutrient deficiencies affected chlorophyll content and generally increased reflectance in the visible (VIS) 400 700 nm and infrared (IR) 700 1100 nm ranges. Magnesium and nitrogen deficiencies had the most pronounced effect on chlorophyll concentration height, and reflectance. All macronutrient deficiencies tested reduced chlorophyll concentration, increase reflectance in the visible range and caused a shift in the position of the red edge (the point of maximum slope on the reflectance spectrum of vegetation between red and near-infrared wavelengths) toward shorter or longer wavelengths; depending upon the element. In the greenhouse, N and Mg induced the greatest increase in reflectance of 33% and 25% in the VI range and 86% and 53% in the IR range, respectively. However, in the growth chamber, an increase of 97% and 25% occurred in the VI range, and 20% and 33% in the IR range, respectively. In the IR range in the growth chamber, P, K, and Ca deficiency caused a reduction in reflectance (412 770 nm

  6. Physicochemical, morphological, thermal and IR spectral changes in the properties of waxy rice starch modified with vinyl acetate.

    PubMed

    Kalita, Dipankar; Kaushik, Neelima; Mahanta, Charu L

    2014-10-01

    Waxy rice starch was modified with vinyl acetate at levels of 4, 6, 8, and 10 % with degree of substitution of 0.021, 0.023, 0.032 and 0.056. The modified starches were studied for physicochemical, morphological, thermal and infra red spectral properties. Waxy starch acetates had high water holding capacity and did not sediment. Scanning electron microscopy revealed surface damage of the granules and their fusion. X ray diffractography showed that crystalline peak intensity had increased on acetylation. Differential scanning calorimetry studies showed changes in thermal properties. While gelatinization temperatures of modified starches were higher than the native starch, their transition enthalpies were lower than the native starch. IR spectra of the starch acetates did not show the peak typical for acetyl group. Thus, modification of waxy rice starch with vinyl acetate caused changes in the starch properties. The high water holding capacity of starch acetates can be exploited for specific applications.

  7. Two-dimensional correlation analysis and waterfall plots for detecting positional fluctuations of spectral changes.

    PubMed

    Ryu, Soo Ryeon; Noda, Isao; Lee, Chang-Hee; Lee, Phil Ho; Hwang, Hyonseok; Jung, Young Mee

    2011-04-01

    In this study, we demonstrate the potentials and pitfalls of using various waterfall plots, such as conventional waterfall plots, two-dimensional (2D) gradient maps, moving window two-dimensional analysis (MW2D), perturbation-correlation moving window two-dimensional analysis (PCMW2D), and moving window principal component analysis two-dimensional correlation analysis (MWPCA2D), in the detection of the existence of band position shifts. Waterfall plots of the simulated spectral datasets are compared with conventional 2D correlation spectra. Different waterfall plots give different features in differentiating the behaviors of frequency shift versus two overlapped bands. Two-dimensional correlation spectra clearly show the very characteristic cluster pattern for both band position shifts and two overlapped bands. The vivid pattern differences are readily detectable in various waterfalls plots. Various types of waterfall plots of temperature-dependent infrared (IR) spectra of ethylene glycol, which does not have the actual band shift but only two overlapped bands, and of Fourier transform infrared (FT-IR) spectra of 2 wt% acetone in a mixed solvent of CHCl(3)/CCl(4) demonstrate that waterfall plots are not able to unambiguously detect the difference between real band shift and two overlapped bands. Thus, the presence or lack of the asynchronous 2D butterfly pattern seems like the most effective diagnostic tool for band shift detection.

  8. Photoinduced adsorption of hydrogen and methane on gamma-alumina. the photoinduced chesorluminescence (PhICL) effect.

    PubMed

    Andreev, N S; Emeline, A V; Polikhova, S V; Ryabchuk, V K; Serpone, N

    2004-01-06

    Adsorption of hydrogen and methane on a preirradiated surface of gamma-Al2O3 produces an afterglow, which has been described as a photoinduced chesorluminescence (PhICL), whose spectral features identify with the intrinsic photoluminescence of alumina. The emission spectrum consists of at least four overlapping single emission bands. For methane adsorption, the PhICL phenomenon is seen only if the solid is preirradiated in the presence of oxygen. Emission decay kinetics of the PhICL effect for gamma-Al2O3 reveal two wavelength regimes: a short wavelength regime at lambda = 300-370 nm (decay time tau = 1.1 +/- 0.2 s; signal width = 2.8 s), and a longer wavelength regime at lambda = 380-700 nm (decay time tau = 2.1 +/- 0.1 s; signal width = 4.3 s). A model is proposed in which there exist two different emission centers and, thus, two different pathways for emission decay. In the first, emission originates with electron trapping by such deep energy traps as anion vacancies {e- + Va --> F+ + hv1} to yield electron F-type color centers, whereas in the second, emission originates from electron/trapped hole recombination {e- + Os*- --> Os2- + hv2}. The first common step of the pathways is homolytic dissociative chemisorption of hydrogen and methane upon interaction with surface-active hole centers Os*-, produced upon preirradiation of alumina, to give atomic hydrogen H* and methyl radicals CH3*. Thermoprogrammed desorption spectra of photoadsorbed or postsorbed oxygen show that adsorbed oxygen interacts with atomic hydrogen and methyl radicals. The products of thermodesorption were H2O for hydrogen and H2O, CO2, and CH3CH3 for methane. The Solonitsyn memory effect coefficient was also evaluated for oxygen photoadsorption.

  9. Gravity-induced absorption changes in Phycomyces blakesleeanus during parabolic flights: first spectral approach in the visible.

    PubMed

    Schmidt, Werner

    2006-12-01

    Gravity-induced absorption changes as experienced during a series of parabolas on the Airbus 300 Zero-G have been measured previously pointwise on the basis of dual-wavelength spectroscopy. Only the two wavelengths of 460 and 665 nm as generated by light-emitting diodes have been utilised during our first two parabolic-flight campaigns. In order to gain complete spectral information throughout the wavelength range from 400 to 900 nm, a miniaturized rapid scan spectrophotometer was designed. The difference of spectra taken at 0 g and 1.8 g presents the first gravity-induced absorption change spectrum measured on wild-type Phycomyces blakesleeanus sporangiophores, exhibiting a broad positive hump in the visible range and negative values in the near infrared with an isosbestic point near 735 nm. The control experiment performed with the stiff mutant A909 of Phycomyces blakesleeanus does not show this structure. These results are in agreement with those obtained with an array spectrophotometer. In analogy to the more thoroughly understood so-called light-induced absorption changes, we assume that gravity-induced absorption changes reflect redox changes of electron transport components such as flavins and cytochromes localised within the plasma membrane.

  10. Macular changes of neuromyelitis optica through spectral-domain optical coherence tomography

    PubMed Central

    Cheng, Lu; Wang, Jing; He, Xu; Xu, Xun; Ling, Zhen-Fen

    2016-01-01

    AIM To evaluate the thickness of the retinal layers in the macula using spectral-domain optical coherence tomography (SD-OCT) in patients with neuromyelitis optica (NMO). METHODS Spectralis SD-OCT, utilizing automated macular layer segmentation, was performed in 26 NMO patients and 26 healthy controls. Visual function including visual field tests and pattern visual evoked potential were recorded in study subjects. RESULTS Forty-one eyes from 26 NMO patients and 52 eyes from 26 age- and sex-matched healthy controls were included. Besides total macular volume, peri-paipillary retinal nerve fiber layer (RNFL) thickness, the thickness of macular RNFL, ganglion cell layer (GCL) and inner plexiform layer (IPL) were also significantly reduced in NMO patients compared to those inhealthy controls (P<0.000). No differences were found in the thickness of macular inner nuclear layer (INL), outer plexiform layer (OPL), and outer nuclear layer (ONL) between the two groups. Reversely, the outer retinal layer (ORL) was shown to be thicker in NMO than controls (P<0.05). Compared with the peri-papillary RNFL thickness, the GCL thickness was demonstrated to correlate with visual function better. CONCLUSION The study provides in vivo evidence of retinal neural loss in NMO patients and demonstrates a better structure-function correlation between retinal ganglion cell and visual function than peri-papillary RNFL does. In addition, no evidence of primary neural damage is found. Besides, the photoreceptor cells and retinal pigments epithelial (RPE) cells presumably proliferated in compensation in NMO after retinal neural loss. PMID:27990369

  11. Retinal ganglion cell complex changes using spectral domain optical coherence tomography in diabetic patients without retinopathy

    PubMed Central

    Hegazy, Ahmed I.; Zedan, Rasha H.; Macky, Tamer A.; Esmat, Soheir M.

    2017-01-01

    AIM To assess the ganglion cell complex (GCC) thickness in diabetic eyes without retinopathy. METHODS Two groups included 45 diabetic eyes without retinopathy and 21 non diabetic eyes. All subjects underwent full medical and ophthalmological history, full ophthalmological examination, measuring GCC thickness and central foveal thickness (CFT) using the RTVue® spectral domain-optical coherence tomography (SD-OCT), and HbA1C level. RESULTS GCC focal loss volume (FLV%) was significantly more in diabetic eyes (22.2% below normal) than normal eyes (P=0.024). No statistically significant difference was found between the diabetic group and the control group regarding GCC global loss volume (GLV%) (P=0.160). CFT was positively correlated to the average, superior and inferior GCC (P=0.001, 0.000 and 0.001 respectively) and negatively correlated to GLV% and FLV% (P=0.002 and 0.031 respectively) in diabetic eyes. C/D ratio in diabetic eyes was negatively correlated to average, superior and inferior GCC (P=0.015, 0.007 and 0.017 respectively). The FLV% was negatively correlated to the refraction and level of HbA1c (P=0.019 and 0.013 respectively) and positively correlated to the best corrected visual acuity (BCVA) in logMAR in diabetic group (P=0.004). CONCLUSION Significant GCC thinning in diabetes predates retinal vasculopathy, which is mainly focal rather than diffuse. It has no preference to either the superior or inferior halves of the macula. Increase of myopic error is significantly accompanied with increased focal GCC loss. GCC loss is accompanied with increased C/D ratio in diabetic eyes. PMID:28393035

  12. CO2 induced climatic change and spectral variations in the outgoing terrestrial infrared radiation

    NASA Technical Reports Server (NTRS)

    Charlock, T. P.

    1984-01-01

    The published temperature changes produced in general circulation model simulations of CO2 induced climate modification are used to compute the top of the atmosphere, clear sky outgoing infrared radiance changes expected for doubled CO2. A significant wavenumber shift is produced, with less radiance emerging in the 500-800 per cm (20.0-12.5 micron) CO2 band and with more emerging in the 800-1200 per cm (12.5-8.3 micron) window. The effect varies greatly with latitude. The radiance shift in the 2300 per cm (4.3 micron) region is of the order of 10-30 percent for doubled CO2. It is suggested that the 2300 per cm region be carefully monitored as an aid in detecting the climatic effects of increasing CO2. The change in the wavenumber-integrated radiant exitance is at most a few percent.

  13. Temperature-induced changes in soft tissues analyzed by spectral methods and transient elastography: A comparative study

    NASA Astrophysics Data System (ADS)

    Cortela, G. A.; Benech, N.; Pereira, W. C. A.; Negreira, C.

    2012-05-01

    Some biological tissues, such as skeletal muscle, have regular or quasi-periodic structures. Periodicity of these structures can be investigated by spectral methods based on ultrasonic backscattered signals. These methods estimate the Mean Scatterer Spacing (MSS). In this work we analyzed the MSS dependence with temperature in bovine skeletal muscle tissue samples. Through spectral analysis we found that the relative variation of the MSS, in the temperature range 20 - 48°C was of ~ 2% /°C. For the same sample and under the same experimental conditions, we analyzed the propagation velocity of shear waves by transient elastography. It was determined that the relative variation of shear elastic modulus was ~ 3% /°C in the same temperature range. The repeatability of the results was tested in three tissue samples, with a set of 6 measurements on each. The relative variation is therefore similar for both parameters. Thus, this study shows that both techniques can be used as a method of noninvasive thermometry for small temperature range. In addition we emphasize the conceptual differences between both methods. As temperature changes, MSS estimation varies due to two physical phenomena. An apparent variation in mean spacing is produced because the sound speed is temperature-dependent, while tissue expansion produces a real change. In practice it is difficult to discriminate the weight of each component in the MSS variation. On the other side, transient elastography is less sensitive to thermal expansion. Thus it measures the actual shear wave speed change with temperature. This differentiation between both methods could be used to construct useful thermoelastic models for soft tissues in the future.

  14. Photo-induced reactions in the ion-molecule complex Mg+-OCNC2H5

    NASA Astrophysics Data System (ADS)

    Sun, Ju-Long; Liu, Haichuan; Han, Ke-Li; Yang, Shihe

    2003-06-01

    Ion-molecule complexes of magnesium cation with ethyl isocyanate were produced in a laser-ablation supersonic expansion nozzle source. Photo-induced reactions in the 1:1 complexes have been studied in the spectral range of 230-410 nm. Photodissociation mass spectrometry revealed the persistent product Mg+ from nonreactive quenching throughout the entire wavelength range. As for the reactive channels, the photoproducts, Mg+OCN and C2H5+, were produced only in the blue absorption band of the complex with low yields. The action spectrum of Mg+(OCNC2H5) consists of two pronounced peaks on the red and blue sides of the Mg+ 32P←32S atomic transition. The ground state geometry of Mg+-OCNC2H5 was fully optimized at B3LYP/6-31+G** level by using GAUSSIAN 98 package. The calculated absorption spectrum of the complex using the optimized structure of its ground state agrees well with the observed action spectrum. Photofragment branching fractions of the products are almost independent of the photolysis photon energy for the 3Px,y,z excitations. The very low branching ratio of reactive products to nonreactive fragment suggests that evaporation is the main relaxation pathway in the photo-induced reactions of Mg+(OCNC2H5).

  15. Detection of retinal changes in Parkinson’s disease with spectral-domain optical coherence tomography

    PubMed Central

    Aaker, Grant D; Myung, Jane S; Ehrlich, Joshua R; Mohammed, Mujtaba; Henchcliffe, Claire; Kiss, Szilárd

    2010-01-01

    Purpose This pilot study investigated whether high-resolution spectral-domain optical coherence tomography (SD-OCT) could detect differences in inner retinal layer (IRL), peripapillary retinal nerve fiber layer (RNFL), and macular thickness between patients with Parkinson’s disease (PD) and controls. Methods Both eyes of patients with PD and age-matched controls were imaged with the Heidelberg Spectralis® HRA + OCT. RNFL, IRL, and macular thickness were measured for each eye using Heidelberg software. These measurements were compared with validated, published normal values for macular and RNFL thickness, and compared with matched controls for IRL thickness. Results Eighteen eyes from nine subjects with PD and 19 eyes of 16 control subjects were evaluated using SD-OCT. The average age of PD patients was 64 years with a range of 52–75 years. The average age of controls was 67 years with a range of 50–81 years. No significant reduction in IRL thickness was detected between PD patients and age-matched controls at 13 points along a 6 mm horizontal section through the fovea. No significant difference in RNFL thickness was detected between PD patients and published normal values. Overall average RNFL thickness was 97 μm for PD patients, which exactly matched the normative database value. However, significant differences in macular thickness were detected in three of nine subfields between PD subjects and published normal values. In PD subjects, the outer superior subfield was 2.8% thinner (P = 0.026), while the outer nasal and inner inferior subfields were 2.8% (P = 0.016) and 2.7% (P = 0.001) thicker compared to published normal values. Conclusion In this pilot study, significant differences in macular thickness were detected in three of nine subfields by SD-OCT. However, SD-OCT did not detect significant reductions in peripapillary RNFL and IRL thickness between PD patients and controls. This suggests that macular thickness measurements by SD-OCT may potentially

  16. EEG Spectral Changes in Treatment Naïve Active Alcoholics

    PubMed Central

    Fein, G.; Allen, J.

    2007-01-01

    Background The present study examines the EEG spectra of actively drinking treatment naïve alcoholics (TxNA). Methods EEGs were gathered on 51 TxNA’s and age and sex-matched controls during eyes-closed conditions. Participants were excluded for lifetime diagnoses of psychiatric or substance abuse disorders. Power for the theta to high beta bands was examined across midline electrodes. Results The TxNA sample exhibited a nexus of disinhibited traits associated with the vulnerability to alcoholism, and had developed alcohol dependence, but no other diagnosable psychiatric or substance abuse disorders. The TxNA subjects evidenced higher power for all EEG bands compared to controls. The magnitude and anterior-posterior extent of the group differences varied across bands. Within the TxNA group, EEG power was negatively correlated with average and peak alcohol drinking duration and average and peak alcohol dose. Conclusions Increased EEG power across the theta to high beta bands distinguishes TxNAs without comorbid diagnoses from controls. These effects varied across bands in their magnitude and spatial extent, suggesting that there are different effects for the different EEG spectral generators. We hypothesize the increased power in these individuals is a trait difference associated with the inherited nexus of disinhibited traits and its manifestation in alcoholism. Based on the strong negative correlations with alcohol use variables, we speculate that decreases in EEG power are a morbid effect of long-term alcohol abuse. We acknowledge that this hypothesized effect of alcohol abuse on EEG power is opposite to the increased EEG power we hypothesize is associated with alcoholism and its inherited nexus of disinhibited traits. An implication of this model is that with continuing alcohol abuse, the increased EEG power in TxNAs will eventually be overpowered by the effects of long-term severe alcohol abuse. This model predicts that in very long-term alcoholics EEG power

  17. Native vs photoinduced chemiluminescence in dimethoate determination.

    PubMed

    Catalá-Icardo, M; López-Paz, J L; Choves-Barón, C; Peña-Bádena, A

    2012-01-13

    The determination of dimethoate using either its native chemiluminescent (CL) properties or its photoinduced chemiluminescence obtained by irradiation with a 15 W low-pressure mercury lamp was studied. Thereby, two flow injection systems (FIA) with and without irradiation were exhaustively optimized and their analytical characteristics studied. Better sensitivity and selectivity was found in absence of irradiation, due to the enhancing effect of hexadecylpyridinium chloride (HPC), which acted as a sensitizer. In the developed FIA-CL system, the alkaline hydrolysis of dimethoate with NaOH was performed on-line in presence of HPC. The oxidation of the product of hydrolysis with Ce(IV) in hydrochloric medium induced chemiluminescence. The method provided a limit of detection of only 0.05 ng mL(-1) without any pre-treatment. However, the combination with solid phase extraction allowed the removal of some potential interferents as well as the preconcentration of the pesticide. Finally, the developed method was successfully applied to natural waters with recoveries between 95 and 108%.

  18. Photoinduced chemiluminescence determination of carbamate pesticides.

    PubMed

    Catalá-Icardo, M; Meseguer-Lloret, S; Torres-Cartas, S

    2016-05-11

    A liquid chromatography method with post-column photoinduced chemiluminescence (PICL) detection is proposed for the simultaneous determination of eight carbamate pesticides, namely aldicarb, butocarboxim, ethiofencarb, methomyl, methiocarb, thiodicarb, thiofanox and thiophanate-methyl. After chromatographic separation, quinine (sensitizer) was incorporated and the flow passed through an UV lamp (67 s of irradiation time) to obtain the photoproducts, which reacted with acidic Ce(iv) and provided a CL emission. The PICL method showed great selectivity for carbamate pesticides containing sulphur in their chemical structure. A solid-phase extraction process increased sensitivity (LODs ranging from 0.06 to 0.27 ng mL(-1)) and allowed the carbamate pesticides in surface and ground water samples to be determined, with recoveries in the range 87-110% (except for thiophanate-methyl, whose recoveries were between 60 and 75%). The intra- and inter-day precision was evaluated, with RSD ranging from 1.1 to 7.5% and from 2.6 to 12.3%, respectively. A discussion about the PICL mechanism is also included.

  19. Photoinduced electron transfer in ordered polymers

    SciTech Connect

    Jones, G. II.

    1991-12-01

    Long range photoinduced electron transfer between electron donor and acceptor groups is of considerable current interest in terms of strategies for artificial photosynthesis and studies regarding the redox properties of proteins. As part of an extensive study of long range electron transfer involving biopolymers, we have carried out this year investigations of the assembly of electron transfer agents in a system of model short peptides. Also studied is a polyelectrolyte that can adopt a helical conformation when electrostatically complexed with organic dye counter-ions. The principal interest in these systems has to do with the well ordered secondary structures adopted by peptide polymers, and the capabilities for synthetic modification of peptide side chains and end groups with chromophores or electroactive substituents. The present report gives a brief account of the following elements of work related to photochemical electron transfer themes: (1) the synthesis and photochemical characterization of chromophore-bound peptides and amino acid model compounds based on the amino acids, tryptophan and the spacer residue, alanine (Ala); (2) the study of binding of the cationic organic dye to a peptide electrolyte, for which cooperative dye loading and helix formation is important; and (3) completion of the synthesis of a new series of acridinium chromophores that have rod-like'' arrangements of inked aryl rings for assembly of electron donor-acceptor systems that will exhibit especially long lived charge separation.

  20. Inactivation of tyrosinase photoinduced by pterin

    SciTech Connect

    Laura Dantola, M.; Gojanovich, Aldana D.; Thomas, Andres H.

    2012-08-03

    Highlights: Black-Right-Pointing-Pointer Under UV-A radiation, tirosinase is photoinactivated by pterin. Black-Right-Pointing-Pointer The mechanism involves an electron transfer-initiated process. Black-Right-Pointing-Pointer The photochemical process affects both activities of tyrosinase. -- Abstract: Tyrosinase catalyzes in mammals the first and rate-limiting step in the biosynthesis of the melanin, the main pigment of the skin. Pterins, heterocyclic compounds able to photoinduce oxidation of DNA and its components, accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder in which the protection against UV radiation fails due to the lack of melanin. Aqueous solutions of tyrosinase were exposed to UV-A irradiation (350 nm) in the presence of pterin, the parent compound of oxidized pterins, under different experimental conditions. The enzyme activity in the irradiated solutions was determined by spectrophotometry and HPLC. In this work, we present data that demonstrate unequivocally that the enzyme is photoinactivated by pterin. The mechanism of the photosensitized process involves an electron transfer from tyrosinase to the triplet excited state of pterin, formed after UV-A excitation of pterin. The biological implications of the results are discussed.

  1. Photo-induced chemical reaction of trans-resveratrol.

    PubMed

    Zhao, Yue; Shi, Meng; Ye, Jian-Hui; Zheng, Xin-Qiang; Lu, Jian-Liang; Liang, Yue-Rong

    2015-03-15

    Photo-induced chemical reaction of trans-resveratrol has been studied. UV B, liquid state and sufficient exposure time are essential conditions to the photochemical change of trans-resveratrol. Three principal compounds, cis-resveratrol, 2,4,6-phenanthrenetriol and 2-(4-hydroxyphenyl)-5,6-benzofurandione, were successively generated in the reaction solution of trans-resveratrol (0.25 mM, 100% ethanol) under 100 μW cm(-2) UV B radiation for 4h. cis-Resveratrol, originated from isomerization of trans-resveratrol, resulted in 2,4,6-phenanthrenetriol through photocyclisation reaction meanwhile loss of 2 H. 2,4,6-Phenanthrenetriol played a role of photosensitizer producing singlet oxygen in the reaction pathway. The singlet oxygen triggered [4+2] cycloaddition reaction of trans-resveratrol, and then resulted in the generation of 2-(4-hydroxyphenyl)-5,6-benzofurandione through photorearrangement and oxidation reaction. The singlet oxygen reaction was closely related to the substrate concentration of trans-resveratrol in solution.

  2. Ultrafast investigation of photoinduced charge transfer in aminoanthraquinone pharmaceutical product

    NASA Astrophysics Data System (ADS)

    Zhang, Song; Sun, Simei; Zhou, Miaomiao; Wang, Lian; Zhang, Bing

    2017-02-01

    We investigated the mechanism of intramolecular charge transfer and the following radiationless dynamics of the excited states of 1-aminoanthraquinone using steady state and time-resolved absorption spectroscopy combined with quantum chemical calculations. Following photoexcitation with 460 nm, conformational relaxation via twisting of the amino group, charge transfer and the intersystem crossing (ISC) processes have been established to be the major relaxation pathways responsible for the ultrafast nonradiative of the excited S1 state. Intramolecular proton transfer, which could be induced by intramolecular hydrogen bonding is inspected and excluded. Time-dependent density functional theory (TDDFT) calculations reveal the change of the dipole moments of the S0 and S1 states along the twisted coordinate of the amino group, indicating the mechanism of twisted intra-molecular charge transfer (TICT). The timescale of TICT is measured to be 5 ps due to the conformational relaxation and a barrier on the S1 potential surface. The ISC from the S1 state to the triplet manifold is a main deactivation pathway with the decay time of 28 ps. Our results observed here have yield a physically intuitive and complete picture of the photoinduced charge transfer and radiationless dynamics in anthraquinone pharmaceutial products.

  3. Diel variations in photoinduced oxidation of Hg0 in freshwater.

    PubMed

    Garcia, Edenise; Poulain, Alexandre J; Amyot, Marc; Ariya, Parisa A

    2005-05-01

    Experiments have been conducted to determine diel variations in photoinduced Hg0 oxidation in lake water under natural Hg0(aq) concentrations. Pseudo-first-order rates of photooxidation (k') were calculated for water freshly collected in a Canadian Shield lake, Lake Croche (45 degrees 56' N, 74 degrees 00' W), at different periods of the day and subsequently incubated in the dark. Hg0 oxidation rates ranged from 0.02 to 0.07 h(-1), increasing from sunrise to noon and then decreasing throughout the remainder of the day. These changes paralleled those in sunlight intensity integrated over 1 h preceding water collection, and suggested that the water freshly collected in daylight was rich in photochemically produced Hg0 oxidants. It was also estimated that under intense solar radiation, even if oxidation rates reached a peak, reduction of Hg(II) was the prevalent redox process. Inversely, Hg0 oxidation overcame DGM production during the night or at periods of weaker light intensity. Overall, these findings explain the decreases in the DGM pool generally observed overnight. They also support previous reports that, during summer days, volatilization of Hg0 from water represent an important step in the Hg cycle in freshwater systems.

  4. Photoinduced isomerization of lycopene and application to tomato cultivation.

    PubMed

    Heymann, Thomas; Raeke, Julia; Glomb, Marcus A

    2013-11-20

    The present study aimed to investigate if growth conditions have an impact on the isomeric composition of lycopene in tomatoes. First a model system for photoinduced isomerization was established. Tomato extracts were irradiated with a halogen lamp, whose wavelength spectrum is close to the spectrum of daylight and thus mimics field-grown cultivation. Different optical filters were interposed between lamp and samples to simulate greenhouse conditions. 5-cis-Lycopene was formed preferentially while the concentration of 7-cis-lycopene decreased in field-grown model systems. The change of isomerization in greenhouse model systems led to a significantly different ratio. Consequently 5-cis- and 7-cis-lycopene were identified as potent markers for the differentiation of various lighting conditions during cultivation. This result was verified in biological samples. Authentic field-grown tomatoes (var. Lycopersicon esculentum Mill. var. commune L. H. Bailey "Harzfeuer") showed a significantly higher content of 5-cis-lycopene 5.90 ± 0.45% compared to tomatoes of the same variety grown under electric lighting 4.11 ± 0.10%. Additionally, the ratio of 7-cis-lycopene was significantly lower under field-grown conditions.

  5. Theoretical approach to photoinduced inhomogeneous anisotropy in bacteriorhodopsin films.

    PubMed

    Acebal, P; Carretero, L; Blaya, S; Murciano, A; Fimia, A

    2007-07-01

    The aim of this work was to perform a complete study of the dynamic and steady-state photoinduced processes of thick bacteriorhodopsin (bR) films, taking into account all the physical parameters and the coupling of rate equations with the energy transfer equation. The theoretical approach was compared with experimental data, and good concordance was found between both sets of data. The theoretical approach shows that the values of the rate constants for solid bR films are about two or three orders of magnitude lower than those observed in solution. It can also be noted that the temperature change during the experiment had a great influence on the final values of transmittance and, consequently, on the inhomogeneous distribution along the coordinate of light propagation. The study shows that, depending on the intensity and wavelength of the pump beam, we can obtain a very inhomogeneous profile of the population densities, which implies an inhomogeneous profile of the birefringence and dichroism. Therefore, this must be taken into account in the applications described for this system.

  6. Photoinduced Giant Dielectric Constant in Lead Halide Perovskite Solar Cells.

    PubMed

    Juarez-Perez, Emilio J; Sanchez, Rafael S; Badia, Laura; Garcia-Belmonte, Germá; Kang, Yong Soo; Mora-Sero, Ivan; Bisquert, Juan

    2014-07-03

    Organic-inorganic lead trihalide perovskites have emerged as an outstanding photovoltaic material that demonstrated a high 17.9% conversion efficiency of sunlight to electricity in a short time. We have found a giant dielectric constant (GDC) phenomenon in these materials consisting on a low frequency dielectric constant in the dark of the order of ε0 = 1000. We also found an unprecedented behavior in which ε0 further increases under illumination or by charge injection at applied bias. We observe that ε0 increases nearly linearly with the illumination intensity up to an additional factor 1000 under 1 sun. Measurement of a variety of samples of different morphologies, compositions, and different types of contacts shows that the GDC is an intrinsic property of MAPbX3 (MA = CH3NH3(+)). We hypothesize that the large dielectric response is induced by structural fluctuations. Photoinduced carriers modify the local unit cell equilibrium and change the polarizability, assisted by the freedom of rotation of MA. The study opens a way for the understanding of a key aspect of the photovoltaic operation of high efficiency perovskite solar cells.

  7. Ultrafast investigation of photoinduced charge transfer in aminoanthraquinone pharmaceutical product

    PubMed Central

    Zhang, Song; Sun, Simei; Zhou, Miaomiao; Wang, Lian; Zhang, Bing

    2017-01-01

    We investigated the mechanism of intramolecular charge transfer and the following radiationless dynamics of the excited states of 1-aminoanthraquinone using steady state and time-resolved absorption spectroscopy combined with quantum chemical calculations. Following photoexcitation with 460 nm, conformational relaxation via twisting of the amino group, charge transfer and the intersystem crossing (ISC) processes have been established to be the major relaxation pathways responsible for the ultrafast nonradiative of the excited S1 state. Intramolecular proton transfer, which could be induced by intramolecular hydrogen bonding is inspected and excluded. Time-dependent density functional theory (TDDFT) calculations reveal the change of the dipole moments of the S0 and S1 states along the twisted coordinate of the amino group, indicating the mechanism of twisted intra-molecular charge transfer (TICT). The timescale of TICT is measured to be 5 ps due to the conformational relaxation and a barrier on the S1 potential surface. The ISC from the S1 state to the triplet manifold is a main deactivation pathway with the decay time of 28 ps. Our results observed here have yield a physically intuitive and complete picture of the photoinduced charge transfer and radiationless dynamics in anthraquinone pharmaceutial products. PMID:28233835

  8. Impact of contact pressure-induced spectral changes on soft-tissue classification in diffuse reflectance spectroscopy: problems and solutions.

    PubMed

    Cugmas, Blaž; Bregar, Maksimilijan; Bürmen, Miran; Pernuš, Franjo; Likar, Boštjan

    2014-03-01

    Review of the existing studies on the contact pressure-induced changes in the optical properties of biological tissues showed that the reported changes in transmittance, reflectance, absorption, and scattering coefficient are vastly inconsistent. In order to gain more insight into the contact pressure-induced changes observed in biomedical applications involving common probe-spectrometer diffuse reflectance measurement setups and provide a set of practical guidelines minimizing the influence of the changes on the analysis of acquired spectra, we conducted a series of in vivo measurements, where the contact pressure was precisely controlled, and the spectral and contact pressure information were acquired simultaneously. Classification of three measurement sites on a human hand, representing the natural variability in the perfusion and structure of the underlying tissue, was assessed by training and evaluating classifiers at different contact pressure levels and for different probe operators. Based on the results, three practical guidelines have been proposed to avoid classification performance degradation. First, the most suitable pressure level should be identified. Second, the pressure level should be kept in a narrow range during the acquisition of spectra. Third, applications utilizing probes equipped with a calibrated spring can use several classifiers trained at different contact pressure levels to improve classification performance.

  9. Power spectral density changes and language lateralization during covert object naming tasks measured with high-density EEG recordings.

    PubMed

    Ramon, C; Holmes, M; Freeman, Walter J; Gratkowski, Maciej; Eriksen, K J; Haueisen, Jens

    2009-01-01

    Our objective was to study changes in EEG time-domain power spectral density (PSDt) and localization of language areas during covert object naming tasks in human subjects with epilepsy. EEG data for subjects with epilepsy were acquired during the covert object naming tasks using a net of 256 electrodes. The trials required each subject to provide the names of common objects presented every 4 seconds on slides. Each trial comprised the 1.0 second before and 3.0 seconds after initial object presentation. PSDt values at baseline and during tasks were calculated in the theta, alpha, beta, low gamma, and high gamma bands. The spatial contour plots reveal that PSDt values during object naming were 10-20% higher than the baseline values for different bands. Language was lateralized to left frontal or temporal areas. In all cases, the Wada test disclosed language lateralization to the left hemisphere as well.

  10. Photo-induced valence change of the sulfur atom in an L-cysteine thin film grown on a silver metal substrate in a saliva-emulated aqueous solution

    NASA Astrophysics Data System (ADS)

    Tsujibayashi, Toru; Azuma, Junpei; Yamamoto, Isamu; Takahashi, Kazutoshi; Kamada, Masao

    2015-04-01

    A thin film of L-cysteine (HSCH2CH(NH2)COOH) is grown on a silver substrate in saliva-emulated aqueous solution. X-ray photoemission spectroscopic measurements have revealed that the sulfur atom shows valence change under IR laser irradiation at 825 nm. The valence change maintains for about a minute at room temperature and more than an hour between 110 and 250 K after stopping the laser irradiation. It is not observed at all at temperatures lower than 110 K. This temperature-dependent behavior indicates that the photo-excited electronic change should be accompanied by a conformational change in the L-cysteine molecule. It is strongly suggested that the reversible valence change of the sulfur atom is applicable to a memory used around room temperature.

  11. Photo-induced valence change of the sulfur atom in an L-cysteine thin film grown on a silver metal substrate in a saliva-emulated aqueous solution

    SciTech Connect

    Tsujibayashi, Toru; Azuma, Junpei; Yamamoto, Isamu; Takahashi, Kazutoshi; Kamada, Masao

    2015-04-27

    A thin film of L-cysteine (HSCH{sub 2}CH(NH{sub 2})COOH) is grown on a silver substrate in saliva-emulated aqueous solution. X-ray photoemission spectroscopic measurements have revealed that the sulfur atom shows valence change under IR laser irradiation at 825 nm. The valence change maintains for about a minute at room temperature and more than an hour between 110 and 250 K after stopping the laser irradiation. It is not observed at all at temperatures lower than 110 K. This temperature-dependent behavior indicates that the photo-excited electronic change should be accompanied by a conformational change in the L-cysteine molecule. It is strongly suggested that the reversible valence change of the sulfur atom is applicable to a memory used around room temperature.

  12. Changes in pigment, spectral transmission and element content of pink chicken eggshells with different pigment intensity during incubation.

    PubMed

    Yu, Yue; Li, Zhanming; Pan, Jinming

    2016-01-01

    Objective. The objective of this study was to investigate changes in pigment, spectral transmission and element content of chicken eggshells with different intensities of pink pigment during the incubation period. We also investigated the effects of the region (small pole, equator and large pole) and pink pigment intensity of the chicken eggshell on the percent transmission of light passing through the chicken eggshells. Method. Eggs of comparable weight from a meat-type breeder (Meihuang) were used, and divided based on three levels of pink pigment (light, medium and dark) in the eggshells. During the incubation (0-21 d), the values of the eggshell pigment (ΔE, L (∗), a (∗), b (∗)) were measured. The percent transmission of light for different regions and intensities of eggshell pigmentation was measured by using the visible wavelength range of 380-780 nm. Result. Three measured indicators of eggshell color, ΔE, L (∗) and a (∗), did not change significantly during incubation. Compared with other regions and pigment intensities, eggshell at the small pole and with light pigmentation intensity showed the highest percent transmission of light. The transmission value varied significantly (P < 0.001) with incubation time. The element analysis of eggshells with different levels of pink pigment showed that the potassium content of the eggshells for all pigment levels decreased significantly during incubation. Conclusion. In summary, pigment intensity and the region of the eggshell influenced the percent transmission of light of eggshell. Differences in the spectral characteristics of different eggshells may influence the effects of photostimulation during the incubation of eggs. All of these results will be applicable for perfecting the design of light intensity for lighted incubation to improve productivity.

  13. Photoinduced electron transfer in layer-by-layer thin solid films containing cobalt oxide nanosheets, porphyrin, and methyl viologen.

    PubMed

    Sasai, R; Kato, Y; Soontornchaiyakul, W; Usami, H; Masumori, A; Norimatsu, W; Fujimura, T; Takagi, S

    2017-02-15

    The well-known layer-by-layer (LbL) method can be used to prepare solid thin films with a controlled electron transfer direction by appropriately stacking metal oxide nanosheets and functional organic ions. In this study, we prepared thin solid films consisting of cobalt oxide nanosheets (CoNSs) as the electron transfer medium, α,β,γ,δ-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP) as the electron donor, and 1,1'-dimethyl-4,4'-bipyridinium or methyl viologen (MV) as the electron acceptor. We investigated the photoinduced electron transfer phenomenon in these films by irradiating them with 450 nm light. Irradiating the LbL thin solid films prepared with the CoNS/TMPyP/CoNS/MV/CoNS sequence under reduced pressure led to the production of a one-electron reduction compound of MV. Hence, photoinduced electron transfer from TMPyP to MV bound to CoNSs occurred in these LbL thin solid films. However, the conduction band of CoNSs, as determined by the photoabsorption spectral and photoelectrochemical measurements, was much higher than the lowest unoccupied molecular orbital level of TMPyP. Our findings indicate that the observed equipotential photoinduced electron transfer was caused by the metallic electron conductivity of CoNSs, which show a unique charge arrangement of Co(3+) and Co(4+). Moreover, it was also found that the observed photoinduced charge separation state has a longer life-time (>5 h) under the reduced conditions.

  14. Quantifying Vegetation Change in Semiarid Environments: Precision and Accuracy of Spectral Mixture Analysis and the Normalized Difference Vegetation Index

    NASA Technical Reports Server (NTRS)

    Elmore, Andrew J.; Mustard, John F.; Manning, Sara J.; Elome, Andrew J.

    2000-01-01

    Because in situ techniques for determining vegetation abundance in semiarid regions are labor intensive, they usually are not feasible for regional analyses. Remotely sensed data provide the large spatial scale necessary, but their precision and accuracy in determining vegetation abundance and its change through time have not been quantitatively determined. In this paper, the precision and accuracy of two techniques, Spectral Mixture Analysis (SMA) and Normalized Difference Vegetation Index (NDVI) applied to Landsat TM data, are assessed quantitatively using high-precision in situ data. In Owens Valley, California we have 6 years of continuous field data (1991-1996) for 33 sites acquired concurrently with six cloudless Landsat TM images. The multitemporal remotely sensed data were coregistered to within 1 pixel, radiometrically intercalibrated using temporally invariante surface features and geolocated to within 30 m. These procedures facilitated the accurate location of field-monitoring sites within the remotely sensed data. Formal uncertainties in the registration, radiometric alignment, and modeling were determined. Results show that SMA absolute percent live cover (%LC) estimates are accurate to within ?4.0%LC and estimates of change in live cover have a precision of +/-3.8%LC. Furthermore, even when applied to areas of low vegetation cover, the SMA approach correctly determined the sense of clump, (i.e., positive or negative) in 87% of the samples. SMA results are superior to NDVI, which, although correlated with live cover, is not a quantitative measure and showed the correct sense of change in only 67%, of the samples.

  15. Spectral characteristics and linear-nonlinear synchronization changes of different EEG frequency bands during the CNV.

    PubMed

    Molnár, Márk; Csuhaj, Roland; Gaál, Zsófia Anna; Czigler, Balázs; Ulbert, István; Boha, Roland; Kondákor, István

    2008-05-01

    During the CNV recorded in a simple auditory working memory task, task-specific decrease of the relative delta band and a transient increase of the absolute theta band were seen, accompanied by an increase of the absolute alpha1 and alpha2 bands in the posterior region. The decreased delta power probably corresponds to increased task-evoked arousal, whereas the transient theta power increase corresponds to working memory demand and possibly to the orienting response. The increased alpha1 and alpha2 power may be a manifestation of a top-down mechanism revealing control over the execution of a response. The area-specific, task-related, and frequency-dependent changes of EEG complexity measures indicate frontally increasing complexity during the early part of the CNV in the beta frequency bands, which underscores the importance of this region in the mechanisms of anticipatory behavior.

  16. Coastline change mapping using a spectral band method and Sobel edge operator

    NASA Astrophysics Data System (ADS)

    Al-Mansoori, Saeed; Al-Marzouqi, Fatima

    2016-10-01

    Coastline extraction has become an essential activity in wake of the natural disasters taking place in some regions such as tsunami, flooding etc. Salient feature of such catastrophes is lack of reaction time available for combating emergency, thus it is the endeavor of any country to develop constant monitoring mechanism of shorelines. This is a challenging task because of the magnitude of changes taking place to the coastline regularly. Previous research findings highlight a need of formulating automation driven methodology for timely and accurate detection of alterations in the coastline impacting sustainability of mankind operating in the coastal zone. In this study, we propose a new approach for automatic extraction of the coastline using remote sensing data. This approach is composed of three main stages. Firstly, classifying pixels of the image into two categories i.e. land and water body by applying two normalized difference indices i.e. Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI). Then, the process of binary conversion of classified image takes place using a local threshold method. Finally, the coastline is extracted by applying Sobel edge operator with a pair of (3×3) kernels. The approach is tested using 2.5m DubaiSat-1 (DS1) and DubaiSat-2 (DS2) images captured to detect and monitor the changes occurring along Dubai coastal zone within a period of six years from 2009 till 2015. Experimental results prove that the approach is capable of extracting the coastlines from DS1 and DS2 images with moderate human interaction. The results of the study show an increase of 6% in Dubai shoreline resulting on account of numerous man-made infrastructure development projects in tourism and allied sectors.

  17. Ultrafast dynamics during the photoinduced phase transition in VO2

    NASA Astrophysics Data System (ADS)

    Wegkamp, Daniel; Stähler, Julia

    2015-12-01

    The phase transition of VO2 from a monoclinic insulator to a rutile metal, which occurs thermally at TC = 340 K, can also be driven by strong photoexcitation. The ultrafast dynamics during this photoinduced phase transition (PIPT) have attracted great scientific attention for decades, as this approach promises to answer the question of whether the insulator-to-metal (IMT) transition is caused by electronic or crystallographic processes through disentanglement of the different contributions in the time domain. We review our recent results achieved by femtosecond time-resolved photoelectron, optical, and coherent phonon spectroscopy and discuss them within the framework of a selection of latest, complementary studies of the ultrafast PIPT in VO2. We show that the population change of electrons and holes caused by photoexcitation launches a highly non-equilibrium plasma phase characterized by enhanced screening due to quasi-free carriers and followed by two branches of non-equilibrium dynamics: (i) an instantaneous (within the time resolution) collapse of the insulating gap that precedes charge carrier relaxation and significant ionic motion and (ii) an instantaneous lattice potential symmetry change that represents the onset of the crystallographic phase transition through ionic motion on longer timescales. We discuss the interconnection between these two non-thermal pathways with particular focus on the meaning of the critical fluence of the PIPT in different types of experiments. Based on this, we conclude that the PIPT threshold identified in optical experiments is most probably determined by the excitation density required to drive the lattice potential change rather than the IMT. These considerations suggest that the IMT can be driven by weaker excitation, predicting a transiently metallic, monoclinic state of VO2 that is not stabilized by the non-thermal structural transition and, thus, decays on ultrafast timescales.

  18. Enhancing Photoinduced Electron Transfer Efficiency of Fluorescent pH-Probes with Halogenated Phenols

    PubMed Central

    2014-01-01

    Photoinduced electron transfer (PET), which causes pH-dependent quenching of fluorescent dyes, is more effectively introduced by phenolic groups than by amino groups which have been much more commonly used so far. That is demonstrated by fluorescence measurements involving several classes of fluorophores. Electrochemical measurements show that PET in several amino-modified dyes is thermodynamically favorable, even though it was not experimentally found, underlining the importance of kinetic aspects to the process. Consequently, the attachment of phenolic groups allows for fast and simple preparation of a wide selection of fluorescent pH-probes with tailor-made spectral properties, sensitive ranges, and individual advantages, so that a large number of applications can be realized. Fluorophores carrying phenolic groups may also be used for sensing analytes other than pH or molecular switching and signaling. PMID:25126834

  19. Photoinduced charge separation by polymer-bound chromophores

    SciTech Connect

    Rodgers, M.A.J.

    1991-09-01

    This project has examined the photodynamic behavior of water-soluble polymers that have covalently linked hydrophobic chromophores spaced along the chains. These polymeric systems have been examined for photoinduced charge separation with electron-accepting ions having different total charge. Focus has been on the excited singlet (S{sub 1}) state formed by laser flash absorption. The effects of pH and ionic strength -- factors that govern the conformational nature of the polymer in solution -- have been studied. A second major effort has been to study photoinduced redox processes involving excited states of water-soluble variants of anthracene and acridine. 27 refs., 16 figs., 2 tabs.

  20. Photo-induced chaos in the Briggs-Rauscher reaction

    NASA Astrophysics Data System (ADS)

    Okazaki, Noriaki; Hanazaki, Ichiro

    1998-07-01

    Discovery of the photo-induced chaos in the Briggs-Rauscher system is reported. The chaotic oscillations were observed between the large- and the small-amplitude simple oscillatory states existent in low and high light intensity regions, respectively. Period-doubling sequence from the large-amplitude oscillations to the chaos was observed. Deterministic nature of the chaos was confirmed by the next-amplitude return map. The stretching and folding mechanism of the trajectories was revealed through the three-dimensional attractor reconstructed via the singular value decomposition method. The chemical origin of the photoinduced chaos is discussed based on the photoautocatalysis of HIO2.

  1. Quantitative analysis of sideband coupling in photoinduced force microscopy

    NASA Astrophysics Data System (ADS)

    Jahng, Junghoon; Kim, Bongsu; Lee, Eun Seong; Potma, Eric Olaf

    2016-11-01

    We present a theoretical and experimental analysis of the cantilever motions detected in photoinduced force microscopy (PiFM) using the sideband coupling detection scheme. In sideband coupling, the cantilever dynamics are probed at a combination frequency of a fundamental mechanical eigenmode and the modulation frequency of the laser beam. Using this detection mode, we develop a method for reconstructing the modulated photoinduced force gradient from experimental parameters in a quantitative manner. We show evidence, both theoretically and experimentally, that the sideband coupling detection mode provides PiFM images with superior contrast compared to images obtained when detecting the cantilever motions directly at the laser modulation frequency.

  2. Crystallization and birefringence studies on fast structural changes followed by non-contact spectral birefringence and Raman spectroscopy techniques

    NASA Astrophysics Data System (ADS)

    Serhatkulu, Toprak Fakr

    2000-11-01

    The structural characteristics of the manufactured polymers such as crystallinity and orientation are controlled by the thermal-deformation history imposed by the processing machinery. Therefore it is essential to monitor these structural characteristics and use the information advantageously to optimize the properties of interest by controlling the process conditions. The focus of this study is to develop robust automated techniques to monitor birefringence and crystallization in real-time. In many of the polymer processing operations involving film stretching where the polymer undergoes a series of thermal deformation treatments, the quantitative changes that take place during the course of these processing operations is poorly understood partly as a result of very rapid structural changes that occur when the polymer's initial condition is not isotropic melt of isotropic solid. There is a great need to quantify the kinetics of the structural changes from preoriented/partially-crystallized states. As part of this dissertation, the birefringence development of preoriented polyethylene terephthalate (PET) films is monitored on-line by the developed spectral birefringence technique with the intent of simulating the heat-setting stage of a tenter film stretching process. Theoretical improvements, software development and optimization, and the equipment design and construction are some of the major tasks accomplished in this dissertation. The automated spectral birefringence technique not only allows the measurement of retardations to very high values, but also enables one to detect the changes in the trend in birefringence (such as a decrease as a result of relaxation, or an increase as a result of crystallization) and to investigate changes that occur very rapidly in the order of a few hundred milliseconds. The effects of stretching conditions on the kinetics of the structural changes in PET films were also investigated using characterization techniques such as

  3. Detecting deforestation with a spectral change detection approach using multitemporal Landsat data: a case study of Kinabalu Park, Sabah, Malaysia.

    PubMed

    Phua, Mui-How; Tsuyuki, Satoshi; Furuya, Naoyuki; Lee, Jung Soo

    2008-09-01

    Tropical deforestation is occurring at an alarming rate, threatening the ecological integrity of protected areas. This makes it vital to regularly assess protected areas to confirm the efficacy of measures that protect that area from clearing. Satellite remote sensing offers a systematic and objective means for detecting and monitoring deforestation. This paper examines a spectral change approach to detect deforestation using pattern decomposition (PD) coefficients from multitemporal Landsat data. Our results show that the PD coefficients for soil and vegetation can be used to detect deforestation using change vector analysis (CVA). CVA analysis demonstrates that deforestation in the Kinabalu area, Sabah, Malaysia has significantly slowed from 1.2% in period 1 (1973 and 1991) to 0.1% in period 2 (1991 and 1996). A comparison of deforestation both inside and outside Kinabalu Park has highlighted the effectiveness of the park in protecting the tropical forest against clearing. However, the park is still facing pressure from the area immediately surrounding the park (the 1 km buffer zone) where the deforestation rate has remained unchanged.

  4. Laser-induced refractive index changes in nanocrystalline diamond membranes.

    PubMed

    Preclíková, Jana; Kromka, Alexander; Rezek, Bohuslav; Malý, Petr

    2010-02-15

    We have observed what we believe to be a new phenomenon in nanocrystalline diamond membranes. The optical thickness of the membrane is changed under laser irradiation, which leads to a spectral shift of interference fringes in the transmission and photoluminescence spectra of high-quality thin self-supporting nanocrystalline membranes. The direction of the spectral shift (red/blue) can be tuned by the ambient air pressure. The effect is reversible and is accompanied by changes in photoluminescence intensity. We interpret the results in terms of the changes in the index of refraction caused by the photoinduced adsorption/desorption of air molecules that subsequently affect the properties of subgap energy states related to the surface and the grain boundaries of the nanocrystals.

  5. A femtosecond study of photoinduced electron transfer from dimethylaniline to coumarin dyes in a cetyltrimethylammonium bromide micelle

    SciTech Connect

    Ghosh, Subhadip; Sahu, Kalyanasis; Mondal, Sudip Kumar; Sen, Pratik; Bhattacharyya, Kankan

    2006-08-07

    Ultrafast photoinduced electron transfer (PET) from N,N-dimethylaniline to coumarin dyes in cetyltrimethylammonium bromide (CTAB) micelle is studied using femtosecond upconversion spectroscopy. The rate of PET in a CTAB micelle is found to be highly nonexponential with components much faster ({approx}10 ps) than the slow components of solvation dynamics. The ultrafast components of electron transfer exhibits a bell-shaped dependence on the free energy change which is similar to the Marcus inversion.

  6. Spectral Changes in the Hyperluminous Pulsar in NGC 5907 as a Function of Super-orbital Phase

    NASA Astrophysics Data System (ADS)

    Fürst, F.; Walton, D. J.; Stern, D.; Bachetti, M.; Barret, D.; Brightman, M.; Harrison, F. A.; Rana, V.

    2017-01-01

    We present broadband, multi-epoch X-ray spectroscopy of the pulsating ultra-luminous X-ray source (ULX) in NGC 5907. Simultaneous XMM-Newton and NuSTAR data from 2014 are best described by a multicolor blackbody model with a temperature gradient as a function of accretion disk radius significantly flatter than expected for a standard thin accretion disk (T(r)\\propto {r}-p, with p={0.608}-0.012+0.014). Additionally, we detect a hard power-law tail at energies above 10 keV, which we interpret as being due to Comptonization. We compare this observation to archival XMM-Newton, Chandra, and NuSTAR data from 2003, 2012, and 2013, and investigate possible spectral changes as a function of phase over the 78-day super-orbital period of this source. We find that observations taken around phases 0.3–0.4 show very similar temperature profiles, even though the observed flux varies significantly, while one observation taken around phase 0 has a significantly steeper profile. We discuss these findings in light of the recent discovery that the compact object is a neutron star and show that precession of the accretion disk or the neutron star can self-consistently explain most observed phenomena.

  7. Ultrafast photo-induced nuclear relaxation of a conformationally disordered conjugated polymer probed with transient absorption and femtosecond stimulated Raman spectroscopies.

    PubMed

    Yu, Wenjian; Donohoo-Vallett, Paul J; Zhou, Jiawang; Bragg, Arthur E

    2014-07-28

    A combination of transient absorption (TAS) and femtosecond stimulated Raman (FSRS) spectroscopies were used to interrogate the photo-induced nuclear relaxation dynamics of poly(3-cyclohexyl,4-methylthiophene) (PCMT). The large difference in inter-ring dihedral angles of ground and excited-state PCMT make it an ideal candidate for studying large-amplitude vibrational relaxation associated with exciton trapping. Spectral shifting in the S1 TA spectra on sub-ps timescales (110 ± 20 and 800 ± 100 fs) is similar to spectroscopic signatures of excited-state relaxation observed with related photoexcited conjugated polymers and which have been attributed to exciton localization and a combination of resonant energy transfer and torsional relaxation, respectively. Measurements made with both techniques reveal fast PCMT S1 decay and triplet formation (τS1 = 25-32 ps), which is similar to the excited-state dynamics of short oligothiophenes and highly twisted polyconjugated molecules. On ultrafast timescales FSRS of S1 PCMT offers a new perspective on the nuclear dynamics that underlie localization of excitons in photoexcited conjugated polymers: Spectral dynamics in the C=C stretching region (1400-1600 cm(-1)) include a red-shift of the in-phase C=C stretching frequency, as well as a change in the relative intensity of in-phase and out-of-phase stretch intensities on a timescale of ∼100 fs. Both changes indicate an ultrafast vibrational distortion that increases the conjugation length in the region of the localized excitation and are consistent with exciton self-localization or trapping. Wavelength-dependent excited-state FSRS measurements further demonstrate that the C=C stretching frequency provides a useful spectroscopic handle for interrogating the degree of delocalization in excited conjugated polymers given the selectivity achieved via resonance enhancement.

  8. Ultrafast photo-induced nuclear relaxation of a conformationally disordered conjugated polymer probed with transient absorption and femtosecond stimulated Raman spectroscopies

    SciTech Connect

    Yu, Wenjian; Donohoo-Vallett, Paul J.; Zhou, Jiawang; Bragg, Arthur E.

    2014-07-28

    A combination of transient absorption (TAS) and femtosecond stimulated Raman (FSRS) spectroscopies were used to interrogate the photo-induced nuclear relaxation dynamics of poly(3-cyclohexyl,4-methylthiophene) (PCMT). The large difference in inter-ring dihedral angles of ground and excited-state PCMT make it an ideal candidate for studying large-amplitude vibrational relaxation associated with exciton trapping. Spectral shifting in the S{sub 1} TA spectra on sub-ps timescales (110 ± 20 and 800 ± 100 fs) is similar to spectroscopic signatures of excited-state relaxation observed with related photoexcited conjugated polymers and which have been attributed to exciton localization and a combination of resonant energy transfer and torsional relaxation, respectively. Measurements made with both techniques reveal fast PCMT S{sub 1} decay and triplet formation (τ{sub S1} = 25–32 ps), which is similar to the excited-state dynamics of short oligothiophenes and highly twisted polyconjugated molecules. On ultrafast timescales FSRS of S{sub 1} PCMT offers a new perspective on the nuclear dynamics that underlie localization of excitons in photoexcited conjugated polymers: Spectral dynamics in the C=C stretching region (1400–1600 cm{sup −1}) include a red-shift of the in-phase C=C stretching frequency, as well as a change in the relative intensity of in-phase and out-of-phase stretch intensities on a timescale of ∼100 fs. Both changes indicate an ultrafast vibrational distortion that increases the conjugation length in the region of the localized excitation and are consistent with exciton self-localization or trapping. Wavelength-dependent excited-state FSRS measurements further demonstrate that the C=C stretching frequency provides a useful spectroscopic handle for interrogating the degree of delocalization in excited conjugated polymers given the selectivity achieved via resonance enhancement.

  9. Specific features of photoconductivity and photoinduced piezoelectricity in AgGaGe3Se8 doped crystals

    NASA Astrophysics Data System (ADS)

    Kityk, I. V.; Myronchuk, G. L.; Parasyuk, O. V.; Krymus, A. S.; Rakus, P.; El-Naggar, A. M.; Albassam, A. A.; Lakshminarayana, G.; Fedorchuk, A. O.

    2017-01-01

    In this work, complex photoconductivity and photo-induced piezoelectricity studies were performed for the AgGaGe3Se8 single crystals doped by In, Sn and Cu with content 5% in weighting units. The principal role of the intrinsic cationic and anionic defects is demonstrated. The photoconductivity and optical absorption spectra show substantial changes of effective energy gap and steepness of absorption edge. The role of optical transitions between the localized states in the presence of Sn, Cu, In impurities is explored. Piezoelectric studies under external laser illumination have shown significant role of dopants on the piezoelectric constants values and their anisotropy. Clear photo-induced jumps were discovered. The discussion is performed within the framework of crystallochemistry analysis and quantum chemical evaluations. Possibility of production of optically operated piezoelectric triggers is proposed.

  10. Wavelength-dependent backscattering measurements for quantitative monitoring of apoptosis, Part 2: early spectral changes during apoptosis are linked to apoptotic volume decrease

    NASA Astrophysics Data System (ADS)

    Mulvey, Christine S.; Zhang, Kexiong; Bobby Liu, Wei-Han; Waxman, David J.; Bigio, Irving J.

    2011-11-01

    Elastic scattering spectroscopy (ESS), in the form of wavelength-dependent backscattering measurements, can be used to monitor apoptosis in cell cultures. Early changes in backscattering upon apoptosis induction are characterized by an overall decrease in spectral slope and begin as early as 10 to 15 min post-treatment, progressing over the next 6 to 8 h. The timescale of early scattering changes is consistent with reports of the onset of apoptotic volume decrease (AVD). Modeling cellular scattering with a fixed distribution of sizes and a decreasing index ratio, as well as an increased contribution of the whole cell to cellular scattering, resulting from increased cytoplasmic density, is also consistent with observed spectral changes. Changes in ESS signal from cells undergoing osmotically-induced volume decrease in the absence of apoptosis were similar, but smaller in magnitude, to those of apoptotic cells. Further, blockage of Cl- channels, which blocks AVD and delays apoptosis, blocked the early scattering changes, indicating that the early scattering changes during apoptosis result, at least partially, from AVD. Work continues to identify the additional sources of early spectral scattering changes that result from apoptosis induction.

  11. Quantification of photoinduced order increase in liquid crystals with naphthopyran guests

    NASA Astrophysics Data System (ADS)

    Rumi, Mariacristina; Cazzell, Seth A.; Kosa, Tamas; Sukhomlinova, Ludmila; Taheri, Bahman; White, Timothy J.; Bunning, Timothy J.

    2016-03-01

    Photoinduced order-increasing phase transitions can occur in dye-liquid crystal mixtures when the photoproduct of the excitation of the dye molecules is more compatible with the liquid crystalline medium than the initial dye species. A detailed investigation of the photoinduced changes of the phase behavior and optical properties of mixtures of liquid crystals with naphthopyran guests upon exposure to light at 365 nm is presented here. In these guest-host systems, the nematic-to-isotropic phase transition temperature is increased upon irradiation. We show that the nematic range can be extended up to 2.9 °C by illumination in 5CB (4 -n -pentyl-4'-cyanobiphenyl) liquid crystal mixtures. The order parameter is significantly increased by illumination at all temperatures within the nematic range and the changes are larger at higher concentrations of the guests. In particular, the illuminated guest-host mixtures exhibit order parameters close to those of the neat liquid crystal host at the same temperature relative to the clearing point. An improved understanding of the photophysical processes taking place at the molecular level in these material systems can inform the design of photoresponsive materials and enhance their potential utility in optical or photonic devices.

  12. [Spectral analysis of the variability of heart rhythm in the analysis of changes in the autonomic regulation during treatment of hypertension with sodium chloride baths].

    PubMed

    Gribanov, A N; Dvornikov, V E

    2001-01-01

    Changes in spectral parameters of heart rate variability were assessed in patients with mild and moderate hypertension (n = 48) and healthy subjects (n = 34) taking sodium chloride bath and in active orthostatic test before and after balneotherapy. Significant changes were not registered. The course of balneotherapy stimulated sympathetic or parasympathetic activity (relative enhancement occurred in 67, absolute in 15% versus 8 and 10% patients, respectively).

  13. The 2005 Accretion Outburst in V1118 Ori: Evidence for A Spectral Change in X-rays

    NASA Astrophysics Data System (ADS)

    Audard, M.; Güdel, M.; Skinner, S. L.; Briggs, K. R.; Walter, F. M.; Stringfellow, G.; Hamilton, R. T.; Guinan, E. F.

    2005-12-01

    We present results from our X-ray monitoring campaign of the 2005 accretion outburst in the young low-mass star V1118 Ori. Optical and near-infrared photometry are presented as well. The X-ray data from early 2005 indicate that the X-ray flux and luminosity varied within a factor of two only, and were similar to the pre-outburst values measured in a serendipitous observation in 2002. Similarly, the hydrogen column density showed no evidence for significant excursions from the pre-outburst value of a few times 1021 cm-2. However, we observed a spectral change from a dominant hot plasma ( ˜ 25 MK) in 2002 and in January 2005 to a cooler plasma ( ˜ 8 MK) in February and March 2005. We argue that the closing in of the accretion disk during the outburst disrupted the hot magnetic loops high in the corona, whereas the lower cooler loops were less affected and became the dominant coronal component. We acknowledge support by NASA through Chandra award DD5-6029X and through XMM-Newton award NNG05GI96G to Columbia University. The Chandra X-ray Observatory Center is operated by the Smithsonian Astrophysical Observatory for and on behalf of the NASA under contract NAS8-03060. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. The PSI group acknowledges support from the Swiss National Science Foundation (grants 20-58827.99 and 20-66875.01). Stony Brook's participation in SMARTS is made possible by support from the offices of the Provost and the Vice President for Research. We thank J. Allyn Smith, P. McGehee, J. Espinoza, and D. Gonzalez for doing the observations with the SMARTS telescopes. We also thank H. Tannanbaum, N. Schartel, and the VLA TOO panel for granting time to observe V1118 Ori.

  14. Photoinduced "stick-slip" on superhydrophilic semiconductor surfaces.

    PubMed

    Denison, Kieth R; Boxall, Colin

    2007-04-10

    Transparent mesoporous TiO2 (M-TiO2) thin films were prepared on quartz via a reverse micelle, sol-gel, spin-coating technique. Films were characterized by atomic force microscopy (AFM) and Raman and UV-vis spectroscopies and were found to be mostly anatase with low surface roughness (Rt approximately 5 nm). The time dependence of film photoinduced superhydrophilicity (PISH) was measured by observation of the spreading of a sessile water drop using a new, continuous measurement technique wherein the drop was first applied to the semiconductor surface and then was filmed while it and the underlying substrate were illuminated by 315 nm ultraband gap light. Results obtained at 100% relative humidity (RH) at 293 K showed that drops on M-TiO2 surfaces exhibited a photoinduced "stick-slip" behavior, the first time such an effect has been observed. The thermodynamic driving force for this photoinduced stick-slip was the departure of the system from capillary equilibrium as, with increasing illumination time, the concentration of surface Ti-OH groups increased and the equilibrium contact angle of the drop, theta0, decreased. A simple theoretical description of photoinduced stick-slip is derived and is used to calculate a value of the potential energy barrier associated with surface inhomogeneities that oppose onset of movement of the triple line, U = 6.63 x 10(-6) J m(-1). This is the first time that U has been quantified for a surface with photoinduced superhydrophilicity. Triple line retreat measurements on an evaporating drop on M-TiO2 in the dark, RH = 60%, T = 293 K, gave a value of U = 9.4 x 10(-6) J m(-1), indicating that U decreases upon UV illumination and that U in the light is primarily associated with inhomogeneities that are unaffected by an increase in the surface Ti-OH population, such as the physical roughness of the surface. In the dark evaporation experiment, the drop was found to retreat with an areal velocity of 1.48 x 10(-8) m2 s(-1). However, under UV

  15. Photo-induced bending in a light-activated polymer laminated composite.

    PubMed

    Mu, Xiaoming; Sowan, Nancy; Tumbic, Julia A; Bowman, Christopher N; Mather, Patrick T; Qi, H Jerry

    2015-04-07

    Light activated polymers (LAPs) have attracted increasing attention since these materials change their shape and/or behavior in response to light exposure, which serves as an instant, remote and precisely controllable stimulus that enables non-contact control of the material shape and behavior through simple variation in light intensity, wavelength and spatially controlled exposure. These features distinguish LAPs from other active polymers triggered by other stimuli such as heat, electrical field or humidity. Previous examples have resulted in demonstrations in applications such as surface patterning, photo-induced shape memory behavior, and photo-origami. However, in many of these applications, an undesirable limitation has been the requirement to apply and maintain an external load during light irradiation. In this paper, a laminated structure is introduced to provide a pre-programmed stress field, which is then used for photo-induced deformation. This laminated structure is fabricated by bonding a stretched elastomer (NOA65) sheet between two LAP layers. Releasing the elastomer causes contraction and introduces a compressive stress in the LAPs, which are relaxed optically to trigger the desired deformation. A theoretical model is developed to quantitatively examine the laminated composite system, allowing exploration of the design space and optimum design of the laminate.

  16. Photo-induced halide redistribution in organic–inorganic perovskite films

    DOE PAGES

    deQuilettes, Dane W.; Zhang, Wei; Burlakov, Victor M.; ...

    2016-05-24

    Organic-inorganic perovskites such as CH3NH3PbI3 are promising materials for a variety of optoelectronic applications, with certified power conversion efficiencies in solar cells already exceeding 21%. Nevertheless, state-of-the-art films still contain performance-limiting non-radiative recombination sites and exhibit a range of complex dynamic phenomena under illumination that remain poorly understood. Here we use a unique combination of confocal photoluminescence (PL) microscopy and chemical imaging to correlate the local changes in photophysics with composition in CH3NH3PbI3 films under illumination. We demonstrate that the photo-induced 'brightening' of the perovskite PL can be attributed to an order-of-magnitude reduction in trap state density. By imaging themore » same regions with time-of-flight secondary-ion-mass spectrometry, we correlate this photobrightening with a net migration of iodine. In conclusion, our work provides visual evidence for photo-induced halide migration in triiodide perovskites and reveals the complex interplay between charge carrier populations, electronic traps and mobile halides that collectively impact optoelectronic performance.« less

  17. Photo-induced halide redistribution in organic-inorganic perovskite films

    NASA Astrophysics Data System (ADS)

    Dequilettes, Dane W.; Zhang, Wei; Burlakov, Victor M.; Graham, Daniel J.; Leijtens, Tomas; Osherov, Anna; Bulović, Vladimir; Snaith, Henry J.; Ginger, David S.; Stranks, Samuel D.

    2016-05-01

    Organic-inorganic perovskites such as CH3NH3PbI3 are promising materials for a variety of optoelectronic applications, with certified power conversion efficiencies in solar cells already exceeding 21%. Nevertheless, state-of-the-art films still contain performance-limiting non-radiative recombination sites and exhibit a range of complex dynamic phenomena under illumination that remain poorly understood. Here we use a unique combination of confocal photoluminescence (PL) microscopy and chemical imaging to correlate the local changes in photophysics with composition in CH3NH3PbI3 films under illumination. We demonstrate that the photo-induced `brightening' of the perovskite PL can be attributed to an order-of-magnitude reduction in trap state density. By imaging the same regions with time-of-flight secondary-ion-mass spectrometry, we correlate this photobrightening with a net migration of iodine. Our work provides visual evidence for photo-induced halide migration in triiodide perovskites and reveals the complex interplay between charge carrier populations, electronic traps and mobile halides that collectively impact optoelectronic performance.

  18. Photo-induced halide redistribution in organic–inorganic perovskite films

    SciTech Connect

    deQuilettes, Dane W.; Zhang, Wei; Burlakov, Victor M.; Graham, Daniel J.; Leijtens, Tomas; Osherov, Anna; Bulovic, Vladimir; Snaith, Henry J.; Ginger, David S.; Stranks, Samuel D.

    2016-05-24

    Organic-inorganic perovskites such as CH3NH3PbI3 are promising materials for a variety of optoelectronic applications, with certified power conversion efficiencies in solar cells already exceeding 21%. Nevertheless, state-of-the-art films still contain performance-limiting non-radiative recombination sites and exhibit a range of complex dynamic phenomena under illumination that remain poorly understood. Here we use a unique combination of confocal photoluminescence (PL) microscopy and chemical imaging to correlate the local changes in photophysics with composition in CH3NH3PbI3 films under illumination. We demonstrate that the photo-induced 'brightening' of the perovskite PL can be attributed to an order-of-magnitude reduction in trap state density. By imaging the same regions with time-of-flight secondary-ion-mass spectrometry, we correlate this photobrightening with a net migration of iodine. In conclusion, our work provides visual evidence for photo-induced halide migration in triiodide perovskites and reveals the complex interplay between charge carrier populations, electronic traps and mobile halides that collectively impact optoelectronic performance.

  19. Photo-induced halide redistribution in organic–inorganic perovskite films

    PubMed Central

    deQuilettes, Dane W.; Zhang, Wei; Burlakov, Victor M.; Graham, Daniel J.; Leijtens, Tomas; Osherov, Anna; Bulović, Vladimir; Snaith, Henry J.; Ginger, David S.; Stranks, Samuel D.

    2016-01-01

    Organic–inorganic perovskites such as CH3NH3PbI3 are promising materials for a variety of optoelectronic applications, with certified power conversion efficiencies in solar cells already exceeding 21%. Nevertheless, state-of-the-art films still contain performance-limiting non-radiative recombination sites and exhibit a range of complex dynamic phenomena under illumination that remain poorly understood. Here we use a unique combination of confocal photoluminescence (PL) microscopy and chemical imaging to correlate the local changes in photophysics with composition in CH3NH3PbI3 films under illumination. We demonstrate that the photo-induced ‘brightening' of the perovskite PL can be attributed to an order-of-magnitude reduction in trap state density. By imaging the same regions with time-of-flight secondary-ion-mass spectrometry, we correlate this photobrightening with a net migration of iodine. Our work provides visual evidence for photo-induced halide migration in triiodide perovskites and reveals the complex interplay between charge carrier populations, electronic traps and mobile halides that collectively impact optoelectronic performance. PMID:27216703

  20. Crystallinity effects on scaling properties of photoinduced modes in silver nanoprisms

    SciTech Connect

    Ng, Ming-Yaw; Ho, I-Lin; Chang, Yia-Chung

    2015-02-21

    The crystallinity effects on scaling properties of photoinduced modes in crystalline silver nanoprisms with C{sub 3v} symmetry are studied using a realistic atomistic model and group theory. Among all vibrational modes, photoinduced modes can be identified as those vibrational modes which possess larger in-phase radial atomic displacement and can be projected out by the projected density of states method. We found that the properties of vibrations in silver nanoprisms strongly depend on the particle’s aspect ratio (bisector length over thickness). By considering crystallinity of silver nanoprisms, the dominant modes with the in-plane oscillation become several closely spaced modes, and become obvious for nanoprisms with a smaller aspect ratio. The oscillation spectra show that the dominant planar modes are insensitive to thickness change. On the contrary, the atomic displacements show significantly different patterns for nanoprisms of different thicknesses. We also found that, for nanoprisms with same aspect ratio that is larger than 4, the vibrational properties of dominant modes exhibit scaling similarity. By using a simple linear transformation, the vibration frequencies for large-sized nanoprisms of aspect ratio 6 can be obtained by a corresponding scaling factor. The calculated results are in good agreement with experimental data.

  1. Classical molecular dynamics simulation of the photoinduced electron transfer dynamics of plastocyanin.

    PubMed Central

    Ungar, L W; Scherer, N F; Voth, G A

    1997-01-01

    Classical molecular dynamics simulations are used to investigate the nuclear motions associated with photoinduced electron transfer in plastocyanin. The blue copper protein is modeled using a molecular mechanics potential; potential parameters for the copper-protein interactions are determined using an x-ray crystallographic structure and absorption and resonance Raman spectra. Molecular dynamics simulations yield a variety of information about the ground (oxidized) and optically excited (charge-transfer) states: 1) The probability distribution of the potential difference between the states, which is used to determine the coordinate and energy displacements, places the states well within the Marcus inverted region. 2) The two-time autocorrelation function of the difference potential in the ground state and the average of the difference potential after instantaneous excitation to the excited state are very similar (confirming linear response in this system); their decay indicates that vibrational relaxation occurs in about 1 ps in both states. 3) The spectral densities of various internal coordinates begin to identify the vibrations that affect the optical transition; the spectral density of the difference potential correlation function should also prove useful in quantum simulations of the back electron transfer. 4) Correlation functions of the protein atomic motions with the difference potential show that the nuclear motions are correlated over a distance of more than 20 A, especially along proposed electron transport paths. Images FIGURE 1 FIGURE 7 PMID:8994588

  2. The time of a photoinduced spin-Peierls phase transition

    SciTech Connect

    Semenov, A. L.

    2015-02-15

    The time τ of the spin-Peierls phase transition is analyzed theoretically as a function of the duration τ{sub p} of the exciting light pulse and the average number x{sub 0} of absorbed photons per magnetic ion after the transmission of the pulse. It is shown that the phase transition occurs at x{sub 0} > x{sub c}. The critical value x{sub c} is determined as a function of the duration τ{sub p} of the light pulse. A photoinduced variation in the optical reflection coefficient R is calculated as a function of time t. The results of calculation are compared with experimental data on ultrafast photoinduced melting of the low-temperature spin-Peierls phase into potassium tetracyanoquinodimethan (K-TCNQ)

  3. Heterodyne technique in photoinduced force microscopy with photothermal effect

    NASA Astrophysics Data System (ADS)

    Yamanishi, J.; Naitoh, Y.; Li, Y. J.; Sugawara, Y.

    2017-03-01

    The heterodyne technique is used to detect short-range forces. Using the heterodyne technique, we demonstrate photoinduced force microscopy (PiFM) imaging and z-spectroscopy without the artifact of photothermal vibration. The rejection ratio was at least 99.975% under a high-scattering condition. In addition, the heterodyne technique employs the optimal amplitude at the first resonance frequency of the cantilever to detect the photoinduced force sensitively. According to our calculation, the optimal ratio of the amplitude to the distance between the dipole of the tip and that of the sample is 0.4448. The heterodyne technique can be employed to perform PiFM without the artifact by using the optimal amplitude.

  4. Photo-induced electron-transfer reactions in heterogeneous media

    NASA Astrophysics Data System (ADS)

    Yang, J. M.

    1981-11-01

    The conversion of solar energy into chemical energy was pursued by two approaches. One is the photo-induced electron transfer reactions in heterogeneous media, and the other is the photo-decomposition of water with liquid-junction solar cells. Photo-induced electron-transfer reactions in heterogeneous media with colloidal silica or poly-acrylate were studied by flash photolysis. In an effort to illustrate that small band-gap semiconductors can be protected from photo-corrosion through surface modification, the surface of polycrystalline ZnO was chemically coated with zinc phthalocyanine and the electron-transfer process across the coated ZnO-electrolyte interface was studied by photo-electrochemical techniques.

  5. Vicinal Difluoroalkylation and Aminosulfonylation of Alkynes under Photoinduced Conditions.

    PubMed

    Xiang, Yuanchao; Li, Yuewen; Kuang, Yunyan; Wu, Jie

    2017-01-23

    A photoinduced vicinal difluoroalkylation and aminosulfonylation of alkynes under photocatalysis was realized. The combination of ethyl 2-bromo-2,2-difluoroacetate, alkynes, and DABCO⋅(SO2 )2 with hydrazines, catalyzed by 9-mes-10-methyl acridinium perchlorate in the presence of visible light, afforded (E)-ethyl 2,2-difluoro-4-aryl-4-sulfamoylbut-3-enoates in good yields with high stereoselectivity. This four-component reaction proceeds through radical addition with the insertion of sulfur dioxide.

  6. A model to predict spatial, spectral and vertical changes in the average cosine of the underwater light fields: Implications for remote sensing of shelf-sea waters

    NASA Astrophysics Data System (ADS)

    Simon, Arthi; Shanmugam, Palanisamy

    2016-03-01

    An optical model is developed using experimental data of Inherent Optical Properties (IOP) from oceanic, coastal and productive lagoon waters in order to calculate vertical and spectral profiles of the average cosine in a wide variety of waters within coastal and shelf-sea environments. The results are compared with those generated using a radiative transfer numerical model based on the invariant imbedding technique (HydroLight) with realistic depth-dependent IOPs and appropriate surface and bottom boundary conditions and the results from three existing models (Haltrin, 1998; Timofeyeva, 1971; Talaulikar et al., 2014). The average cosine predicted by the new model shows good agreement with the values obtained directly from radiative transfer calculations for a broad range of the IOPs and solar zenith conditions. Good correlations with excellent linearity with significantly low errors demonstrate a good deal of confidence of the model for accomplishing further applications. Since knowledge of spatial and temporal structures of the average cosine is of great importance to our understanding of the particle dynamics of pelagic ecosystems and coastal processes, efforts were made to apply the present model to both multispectral MODIS-Aqua imagery and hyperspectral (HICO) images acquired over the Arabian Sea and coastal lagoons of the Bay of Bengal dominated by river plumes and phytoplankton blooms. Maps of the average cosine derived from these data demonstrated significant changes in the magnitude and spectral behavior of the average cosine (from nearly featureless to strong spectral features and inflections) from different water types. Substantial changes in its spatial and spectral structures associated with highly productive waters, phytoplankton blooms and sediment plumes, as compared with open ocean areas, are well supported by the theoretical and experimental studies. The advantages of the new model in comparison with existing models are its capability to predict

  7. Photoreceptor Processing Speed and Input Resistance Changes during Light Adaptation Correlate with Spectral Class in the Bumblebee, Bombus impatiens

    PubMed Central

    Skorupski, Peter; Chittka, Lars

    2011-01-01

    Colour vision depends on comparison of signals from photoreceptors with different spectral sensitivities. However, response properties of photoreceptor cells may differ in ways other than spectral tuning. In insects, for example, broadband photoreceptors, with a major sensitivity peak in the green region of the spectrum (>500 nm), drive fast visual processes, which are largely blind to chromatic signals from more narrowly-tuned photoreceptors with peak sensitivities in the blue and UV regions of the spectrum. In addition, electrophysiological properties of the photoreceptor membrane may result in differences in response dynamics of photoreceptors of similar spectral class between species, and different spectral classes within a species. We used intracellular electrophysiological techniques to investigate response dynamics of the three spectral classes of photoreceptor underlying trichromatic colour vision in the bumblebee, Bombus impatiens, and we compare these with previously published data from a related species, Bombus terrestris. In both species, we found significantly faster responses in green, compared with blue- or UV-sensitive photoreceptors, although all 3 photoreceptor types are slower in B. impatiens than in B. terrestris. Integration times for light-adapted B. impatiens photoreceptors (estimated from impulse response half-width) were 11.3±1.6 ms for green photoreceptors compared with 18.6±4.4 ms and 15.6±4.4 for blue and UV, respectively. We also measured photoreceptor input resistance in dark- and light-adapted conditions. All photoreceptors showed a decrease in input resistance during light adaptation, but this decrease was considerably larger (declining to about 22% of the dark value) in green photoreceptors, compared to blue and UV (41% and 49%, respectively). Our results suggest that the conductances associated with light adaptation are largest in green photoreceptors, contributing to their greater temporal processing speed. We suggest that the

  8. Short- and long-term variability of spectral solar UV irradiance at Thessaloniki, Greece: effects of changes in aerosols, total ozone and clouds

    NASA Astrophysics Data System (ADS)

    Fountoulakis, Ilias; Bais, Alkiviadis F.; Fragkos, Konstantinos; Meleti, Charickleia; Tourpali, Kleareti; Zempila, Melina Maria

    2016-03-01

    In this study, we discuss the short- and the long-term variability of spectral UV irradiance at Thessaloniki, Greece, using a long, quality-controlled data set from two Brewer spectrophotometers. Long-term changes in spectral UV irradiance at 307.5, 324 and 350 nm for the period 1994-2014 are presented for different solar zenith angles and discussed in association with changes in total ozone column (TOC), aerosol optical depth (AOD) and cloudiness observed in the same period. Positive changes in annual mean anomalies of UV irradiance, ranging from 2 to 6 % per decade, have been detected both for clear- and all-sky conditions. The changes are generally greater for larger solar zenith angles and for shorter wavelengths. For clear-skies, these changes are, in most cases, statistically significant at the 95 % confidence limit. Decreases in the aerosol load and weakening of the attenuation by clouds lead to increases in UV irradiance in the summer, of 7-9 % per decade for 64° solar zenith angle. The increasing TOC in winter counteracts the effect of decreasing AOD for this particular season, leading to small, statistically insignificant, negative long-term changes in irradiance at 307.5 nm. Annual mean UV irradiance levels are increasing from 1994 to 2006 and remain relatively stable thereafter, possibly due to the combined changes in the amount and optical properties of aerosols. However, no statistically significant corresponding turning point has been detected in the long-term changes of AOD. The absence of signatures of changes in AOD in the short-term variability of irradiance in the UV-A may have been caused by changes in the single scattering albedo of aerosols, which may counteract the effects of changes in AOD on irradiance. The anti-correlation between the year-to-year variability of the irradiance at 307.5 nm and TOC is clear and becomes clearer as the AOD decreases.

  9. Photoinduced 2-way electron transfer in composites of metal nanoclusters and semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Mondal, Navendu; Paul, Sneha; Samanta, Anunay

    2016-07-01

    In order to explore the potential of nanocomposites comprising semiconductor quantum dots (QDs) and metal nanoclusters (NCs) in photovoltaic and catalytic applications, the interaction between CdTe QDs and gold NCs, Au10 and Au25, stabilized by histidine, bovine serum albumin (BSA) and glutathione, is studied by an ultrafast transient absorption (TA) technique. Temporal and spectral studies of the transients reveal photoinduced 2-way electron transfer between the two constituents of the nanocomposites, where Au NCs, which generally act as electron donors when used as photosensitizers, perform the role of the efficient electron acceptor. Interestingly, it is found that the electron transfer dynamics in these composites is governed not by the distance of separation of the constituents but by the nature of the surface capping ligands. Despite a large separation between the QDs and NCs in a giant BSA-capped system, a higher electron transfer rate in this composite suggests that unlike other smaller capping agents, which act more like insulators, BSA allows much better electron conduction, as indicated previously.In order to explore the potential of nanocomposites comprising semiconductor quantum dots (QDs) and metal nanoclusters (NCs) in photovoltaic and catalytic applications, the interaction between CdTe QDs and gold NCs, Au10 and Au25, stabilized by histidine, bovine serum albumin (BSA) and glutathione, is studied by an ultrafast transient absorption (TA) technique. Temporal and spectral studies of the transients reveal photoinduced 2-way electron transfer between the two constituents of the nanocomposites, where Au NCs, which generally act as electron donors when used as photosensitizers, perform the role of the efficient electron acceptor. Interestingly, it is found that the electron transfer dynamics in these composites is governed not by the distance of separation of the constituents but by the nature of the surface capping ligands. Despite a large separation

  10. VIIRS S-NPP Nighttime DNB Spectral Response Function (SRF): The At-launch Characteristics and How the SRF Changes with Time Due to Tungsten Oxides Chromaticity

    NASA Astrophysics Data System (ADS)

    Guenther, B.; Lei, N.; Moeller, C.

    2015-12-01

    The VIIRS Day-Night Band (DNB) is designed with 3 gain stages: Low (LGS), Mid (MGS) and High (HGS) to span bright daytime to moonlit night earth scene signal levels. The published at-launch DNB relative spectral response (RSR) is based upon the LGS spectral measurements, since it was well measured in the pre-launch test program and the LGS can be calibrated by the on-board solar diffuser (MGS and HGS saturate on the SD). The LGS RSR however does not fully represent the spectral characteristics of nighttime DNB data from the MGS and HGS. Nighttime data users who apply the detailed DNB spectral characteristics in their analyses should use modulated RSR appropriate to the MGS and HGS observations. The RSR modulation is due to spectral darkening of the 4 mirrors of the S-NPP VIIRS telescope, which were contaminated with tungsten oxides in fabrication. These tungsten oxides are 'in family' with transition lenses on eyeglasses that darken when exposed to sunlight but do not recover when VIIRS goes into darkness because VIIRS in space is in a vacuum (transition lenses require atmospheric oxygen to recover). The on-going mirror darkening has caused a time-dependent shift in DNB RSR towards blue wavelengths. This presentation will provide access to the correct RSR to use for S-NPP DNB nighttime data over the mission time on-orbit. The changes in characteristics will be described in engineering terms to facilitate clear user understanding of how to handle RSR for nighttime observations over the mission lifetime.

  11. Cystic macular oedema on spectral-domain optical coherence tomography in choroideremia patients without cystic changes on fundus examination

    PubMed Central

    Genead, M A; Fishman, G A

    2011-01-01

    Purpose To determine the prevalence of cystic macular oedema (CME) in patients with choroideremia (CHM) by using spectral-domain optical coherence tomography (SD-OCT). Methods A total 16 patients affected with CHM were enroled in the study. All patients underwent a complete eye examination. SD-OCT was performed using an OPKO spectral-domain OCT/SLO instrument. Results The average age of the study patients was 44.0±16.0 years (range, 13–63 years). Out of the 16 patients with CHM, 10 patients (62.5%) showed a degree of CME on SD-OCT testing in at least one eye, and 8 patients (50%) showed CME in both eyes. Conclusions Because of its notable prevalence, it would seem prudent to screen CHM patients by SD-OCT for the possible presence of CME and to identify those amenable to future treatment strategies for their macular oedema. PMID:20966974

  12. Spectral and Spread Spectral Teleportation

    SciTech Connect

    Humble, Travis S

    2010-01-01

    We report how quantum information encoded into the spectral degree of freedom of a single-photon state is teleported using a finite spectrally entangled biphoton state. We further demonstrate how the bandwidth of a teleported waveform can be controllably and coherently dilated using a spread spectral variant of teleportation. We present analytical fidelities for spectral and spread spectral teleportation when complex-valued Gaussian states are prepared using a proposed experimental approach, and we discuss the utility of these techniques for integrating broad-bandwidth photonic qubits with narrow-bandwidth receivers in quantum communication systems.

  13. Spectral components of human cardiovascular responses to step changes in Lower Body Negative Pressure (LBNP) before and after 22 hour of 6 deg head down bed rest

    NASA Technical Reports Server (NTRS)

    Knapp, C. F.; Evans, J. M.; Grande, K. J.; Murphy, C. D.; Patwardhan, A. R.

    1992-01-01

    Changes in autonomic outflow to peripheral organs during the development of bedrest induced orthostatic intolerance have not been determined. Recent studies have indicated that spectral analysis provides an indirect assessment of these changes. Eight male subjects were studied before and after 22 hours of 6 degree head down bedrest plus Lasix (40 mg. P.P.). Cardiovascular spectra (using an autoregressive technique) were determined for heart rate (HR, ECG), arterial pressure (AP, Finapres), radial artery flow (RF, Hokansen) and respiration rate (RR, BoMed). Spectra were obtained from 2.5 minute segments during control, lower body negative pressure (minus 10, 20, 30, 40, 50 mmHg) and recovery. Bedrest increased HR spectra power in the low frequency (.001 to .041 Hz) range, increased RF power in the low and mid (.04 to .18 Hz) range and increased AP power in the high (.18 to .50 Hz) frequency range. Increasing levels of lower body negative pressure decreased HR power and increased RF power in the high frequency range and decreased AP power in the low frequency range. Since spectral power of HR in the high frequency range has been shown to indicate parasympathetically mediated regulation and power in the low and mid frequency ranges indicates a sympathetic / parasympathetic mixture, then both bedrest and lower body negative pressure appeared to shift sympathetic / parasympathetic balance toward sympathetic regulation of HR. The interpretation of the spectral content of AP and RF with respect to their autonomic origins remains unclear.

  14. Dependence of photoinduced bending behavior of diarylethene crystals on irradiation wavelength of ultraviolet light.

    PubMed

    Kitagawa, Daichi; Tanaka, Rika; Kobatake, Seiya

    2015-11-07

    The dependence of the photoinduced bending behavior of diarylethene crystals on the ultraviolet light irradiation wavelength was investigated. When irradiated with 365 nm light, a crystal of 1,2-bis(5-methyl-2-phenyl-4-thiazolyl)perfluorocyclopentene (1a) bends toward the incident light. On the other hand, when irradiated with 380 nm light, the crystal of 1a first bends away from the light source and then bends toward the incident light. To explain this bending behavior, we propose a comprehensive mechanism based on the depth of the photochromic reaction from the crystal surface. This mechanism is successfully supported by the change of cell parameters associated with the photochromic reaction upon irradiation with 380 nm light, which was determined by in situ X-ray crystallographic analysis.

  15. Direct and real time probe of photoinduced structure transition in colossal magnetoresistive material

    DOE PAGES

    Li, Junjie; Wang, Xuan; Zhou, Haidong; ...

    2016-07-29

    Here, we report a direct and real time measurement of photoinduced structure phase transition in single crystal La0.84Sr0.16MnO3 using femtosecond electron diffraction. The melting of orthorhombic lattice ordering under femtosecond optical excitation is found involving two distinct processes with different time scales, an initial fast melting of orthorhombic phase in about 4 ps and a subsequent slower transformation in 90 ps and longer timescales. Furthermore, the fast process is designated as the initial melting of orthorhombic phase induced by the Mn-O bond change that is most likely driven by the quenching of the dynamic Jahn-Teller distortion following the photo-excitation. Wemore » attribute the slow process to the growing of newly formed structure domain from the photo-excited sites to the neighboring non-excited orthorhombic sites.« less

  16. Surface modification of ultra high molecular weight polyethylene fibers via the sequential photoinduced graft polymerization

    NASA Astrophysics Data System (ADS)

    Li, Zhi; Zhang, Wei; Wang, Xinwei; Mai, Yongyi; Zhang, Yumei

    2011-06-01

    In this study, a sequential photoinduced graft polymerization process was proposed to improve the poor interfacial bonding property of ultra high molecular weight polyethylene (UHMWPE) fibers. The polymerization was initiated by dormant semipinacol (SP) groups and carried out in a thin liquid layer. Methacrylic acid (MAA) and acryl amide (AM) were grafted stepwise onto the surface of UHMWPE fibers. Attenuated total reflectance infrared spectroscopy (ATR-IR) and thermo gravimetric analysis (TGA) confirmed the grafting. The analysis result of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) indicated the structure of grafted chains. Scanning electron microscopy (SEM) images and atomic force microscopy (AFM) images revealed the apparent morphology changing, and the grafted layers were observed. Interfacial shear stress (IFSS) test of the modified fibers showed an extensively improved interfacial bonding property. The active groups grafted onto the fibers would supply enough anchor points for the chemical bonding with various resins or further reactions.

  17. Direct and real time probe of photoinduced structure transition in colossal magnetoresistive material

    NASA Astrophysics Data System (ADS)

    Li, Junjie; Wang, Xuan; Zhou, Haidong; Zhou, Jun; Cheng, J. G.; Cao, Jianming

    2016-07-01

    We report a direct and real time measurement of photoinduced structure phase transition in single crystal La0.84Sr0.16MnO3 using femtosecond electron diffraction. The melting of orthorhombic lattice ordering under femtosecond optical excitation is found involving two distinct processes with different time scales, an initial fast melting of orthorhombic phase in about 4 ps and a subsequent slower transformation in 90 ps and longer timescales. The fast process is designated as the initial melting of orthorhombic phase induced by the Mn-O bond change that is most likely driven by the quenching of the dynamic Jahn-Teller distortion following the photo-excitation. The slow process is attributed to the growing of newly formed structure domain from the photo-excited sites to the neighboring non-excited orthorhombic sites.

  18. Photo-induced persistent inversion of germanium in a 200-nm-deep surface region.

    PubMed

    Prokscha, T; Chow, K H; Stilp, E; Suter, A; Luetkens, H; Morenzoni, E; Nieuwenhuys, G J; Salman, Z; Scheuermann, R

    2013-01-01

    The controlled manipulation of the charge carrier concentration in nanometer thin layers is the basis of current semiconductor technology and of fundamental importance for device applications. Here we show that it is possible to induce a persistent inversion from n- to p-type in a 200-nm-thick surface layer of a germanium wafer by illumination with white and blue light. We induce the inversion with a half-life of ~12 hours at a temperature of 220 K which disappears above 280 K. The photo-induced inversion is absent for a sample with a 20-nm-thick gold capping layer providing a Schottky barrier at the interface. This indicates that charge accumulation at the surface is essential to explain the observed inversion. The contactless change of carrier concentration is potentially interesting for device applications in opto-electronics where the gate electrode and gate oxide could be replaced by the semiconductor surface.

  19. Control of photoinduced fluorescence enhancement of colloidal quantum dots using metal oxides

    NASA Astrophysics Data System (ADS)

    Sadeghi, Seyed M.; Wing, Waylin J.; Patty, Kira; Campbell, Quinn

    2015-10-01

    It is well known that irradiation of colloidal quantum dots can dramatically enhance their emission efficiencies, leading to so-called photoinduced fluorescence enhancement (PFE). This process is the result of the photochemical and photophysical properties of quantum dots and the way they interact with the environment in the presence of light. It has been shown that such properties can be changed significantly using metal oxides. Using spectroscopic techniques, in this paper we investigate emission of different types of quantum dots (with and without shell) in the presence of metal oxides with opposing effects. We observed significant increase of PFE when quantum dots are deposited on about one nanometer of aluminum oxide, suggesting such oxide can profoundly increase quantum yield of such quantum dots. On the other hand, copper oxide can lead to significant suppression of emission of quantum dots, making them nearly completely dark instantly.

  20. Direct and real time probe of photoinduced structure transition in colossal magnetoresistive material

    SciTech Connect

    Li, Junjie; Wang, Xuan; Zhou, Haidong; Zhou, Jun; Cheng, J. G.; Cao, Jianming

    2016-07-29

    Here, we report a direct and real time measurement of photoinduced structure phase transition in single crystal La0.84Sr0.16MnO3 using femtosecond electron diffraction. The melting of orthorhombic lattice ordering under femtosecond optical excitation is found involving two distinct processes with different time scales, an initial fast melting of orthorhombic phase in about 4 ps and a subsequent slower transformation in 90 ps and longer timescales. Furthermore, the fast process is designated as the initial melting of orthorhombic phase induced by the Mn-O bond change that is most likely driven by the quenching of the dynamic Jahn-Teller distortion following the photo-excitation. We attribute the slow process to the growing of newly formed structure domain from the photo-excited sites to the neighboring non-excited orthorhombic sites.

  1. Dynamics of photoinduced processes in liquid-crystal polymer films containing azo compounds

    SciTech Connect

    Simonov, A N; Larichev, A V

    1999-07-31

    The photoinduced processes in azo-compound-containing side-chain polymer films with liquid-crystal properties are examined theoretically. A model is proposed whereby it is possible to consider the dynamics of the optical response of a medium taking into account the anisotropic saturation in the angular distribution of the azo-dye isomers as well as the intermolecular interaction. The influence of the liquid-crystal ordering in the polymer is taken into account by introducing a phenomenological mean-field factor. Analytical solutions describing changes in the optical properties of a polymer film during the initial illumination stages are in good agreement with experimental data. (this issue is dedicated to the memory of s a akhmanov)

  2. An Explanation of the Photoinduced Giant Dielectric Constant of Lead Halide Perovskite Solar Cells.

    PubMed

    Almond, Darryl P; Bowen, Chris R

    2015-05-07

    A photoinduced giant dielectric constant of ~10(6) has been found in impedance spectroscopy measurements of lead halide perovskite solar cells. We report similar effects in measurements of a porous lead zirconate titanate (PZT) sample saturated with water. The principal effect of the illumination of the solar cell and of the introduction of water into the pore volume of the PZT sample is a significant increase in conductivity and dielectric loss. This is shown to exhibit low frequency power law dispersion. Application of the Kramers-Kronig relationships show the large measured values of permittivity to be related to the power law changes in conductivity and dielectric loss. The power law dispersions in the electrical responses are consistent with an electrical network model of microstructure. It is concluded that the high apparent values of permittivity are features of the microstructural networks and not fundamental effects in the two perovskite materials.

  3. Looking at Photoinduced Charge Transfer Processes in the IR: Answers to Several Long-Standing Questions.

    PubMed

    Dereka, Bogdan; Koch, Marius; Vauthey, Eric

    2017-02-21

    Because of its crucial role in many areas of science and technology, photoinduced electron transfer is the most investigated photochemical reaction. Despite this, several important questions remain open. We present recent efforts to answer some of them, which concern both inter- and intramolecular processes. The decisive factor that allowed these issues to be successfully addressed was the use of time-resolved infrared (TRIR) spectroscopy. Many different transient species, such as tight and loose ion pairs (TIPs and LIPs) and exciplexes, have been invoked to explain the dynamics of intermolecular photoinduced charge separation reactions (i.e., electron transfer between two neutral species) and the production of free ions. However, their structures are essentially unknown, and their exact roles in the reaction mechanism are unclear. Indeed, the commonly used transient electronic absorption spectroscopy does not give much structural insight and cannot clearly distinguish ion pairs from free ions, at least in the visible region. Unambiguous spectral signatures of TIPs, LIPs, and exciplexes could be observed in the IR using electron donor/acceptor (D/A) pairs with adequate vibrational marker modes. The ability to spectrally distinguish these intermediates allowed their dynamics to be disentangled and their roles to be determined. Structural information could be obtained using polarization-resolved TRIR spectroscopy. Our investigations reveal that moderately to highly exergonic reactions result in the formation of both TIPs and LIPs. TIPs are not only generated upon direct charge-transfer excitation of DA complexes, as usually assumed, but are also formed upon static quenching with reactant pairs at distances and orientations enabling charge separation without diffusion. On the other hand, dynamic quenching produces primarily LIPs. In the case of highly exergonic reactions, strong indirect evidence for the generation of ion pairs in an electronic excited state was found

  4. L1-Spanish speakers' acquisition of the English /i/-/I/ contrast II: perception of vowel inherent spectral change.

    PubMed

    Morrison, Geoffrey Stewart

    2009-01-01

    L1-Spanish learners of English have been reported to distinguish English /i/ and /I? on the basis of duration cues, whereas L1-English listeners primarily use spectral cues. Morrison (2008a) hypothesized that duration-based perception is a secondary developmental stage that emerges from an initial stage of multidimensional-category-goodness assimilation of tokens of English /i/ and /I/ to Spanish /i/, with English vowel tokens perceived to be good examples of Spanish /i/ labeled as English /I/ and poor examples labeled as English /i/.

  5. Photoinduced ordering and anchoring properties of azo-dye films.

    PubMed

    Kiselev, Alexei D; Chigrinov, Vladimir; Huang, Dan Ding

    2005-12-01

    We study both theoretically and experimentally the anchoring properties of photoaligning azo-dye films in contact with a nematic liquid crystal depending on the photoinduced ordering of azo-dye molecules. In the mean field approximation, we found that the bare surface anchoring energy depends linearly on the azo-dye order parameter and the azimuthal anchoring strength decays to zero in the limit of vanishing photoinduced ordering. From the absorption dichroism spectra measured in azo-dye films that are prepared from an azo-dye derivative with polymerizable terminal groups we obtain the dependence of the dichroic ratio on the irradiation dose. We also measure the polar and azimuthal anchoring strengths in nematic liquid crystal (NLC) cells aligned by the azo-dye films and derive the anchoring strengths as functions of the dichroic ratio, which is proportional to the photoinduced order parameter. Although linear fitting of the experimental data for both anchoring strengths gives reasonable results, it, predicts vanishing of the azimuthal anchoring strength at some nonzero value of the azo-dye order parameter, in contradiction with theory. By using a simple phenomenological model we show that this discrepancy can be attributed to the difference between the surface and bulk order parameters in the films. The measured polar anchoring energy is found to be an order of magnitude higher than the azimuthal strength. Our theory suggests that the quadrupole term of the spherical harmonics expansion for the azo-dye-NLC intermolecular potential might be of importance for the understanding of this difference.

  6. Photoinduced electron transfer across molecular bridges: electron- and hole-transfer superexchange pathways.

    PubMed

    Natali, Mirco; Campagna, Sebastiano; Scandola, Franco

    2014-06-21

    Photoinduced electron transfer plays key roles in many areas of chemistry. Superexchange is an effective model to rationalize photoinduced electron transfer, particularly when molecular bridges between donor and acceptor subunits are present. In this tutorial review we discuss, within a superexchange framework, the complex role played by the bridge, with an emphasis on differences between thermal and photoinduced electron transfer, oxidative and reductive photoinduced processes, charge separation and charge recombination. Modular bridges are also considered, with specific attention to the distance dependence of donor-acceptor electronic coupling and electron transfer rate constants. The possibility of transition, depending on the bridge energetics, from coherent donor-acceptor electron transfer to incoherent charge injection and hopping through the bridge is also discussed. Finally, conceptual analogies between bridge effects in photoinduced electron transfer and optical intervalence transfer are outlined. Selected experimental examples, instrumental to illustration of the principles, are discussed.

  7. Photoinduced underwater superoleophobicity of TiO2 thin films.

    PubMed

    Sawai, Yusuke; Nishimoto, Shunsuke; Kameshima, Yoshikazu; Fujii, Eiji; Miyake, Michihiro

    2013-06-11

    The photoinduced wettabilities of water, n-hexadecane, dodecane, and n-heptane on a flat TiO2 surface prepared by a sol-gel method-based coating were investigated. An amphiphilic surface produced by UV irradiation exhibited underwater superoleophobicity with an extremely high static oil contact angle (CA) of over 160°. The TiO2 surface almost completely repelled the oil droplet in water. A robust TiO2 surface with no fragile nanomicrostructure was fabricated on a Ti mesh with a pore size of approximately 150 μm. The fabricated mesh was found to be applicable as an oil/water separation filter.

  8. Distance dependence in photo-induced intramolecular electron transfer

    NASA Astrophysics Data System (ADS)

    Larsson, Sven; Volosov, Andrey

    1986-09-01

    The distance dependence of the rate of photo-induced electron transfer reactions is studied. A quantum mechanical method CNDO/S is applied to a series of molecules recently investigated by Hush et al. experimentally. The calculations show a large interaction through the saturated bridge which connects the two chromophores. The electronic matrix element HAB decreases a factor 10 in about 4 Å. There is also a decrease of the rate due to less exothermicity for the longer molecule. The results are in fair agreement with the experimental results.

  9. Photo-induced transmittance in copper selenide nanowires

    NASA Astrophysics Data System (ADS)

    Statkutė, G.; Mikulskas, I.; Jagminas, A.; Tomašiūnas, R.

    2008-01-01

    Photo-induced transmission was investigated in Cu 1.7Se nanowires electrochemically deposited in alumina matrix pores with a central channel of the diameters of 12, 15 and 60 nm by means of the degenerate picosecond pump-probe technique at 1.064 μm wavelength. Resonant excitation intensity dependencies were interpreted. Absorption saturation was ascertained as a result of the drain of acceptor shallow centers. The estimated absorption cross-section was 10 -12 cm 2, saturation intensity - was 1-10 mJ cm -2.

  10. Photoinduced electron transfer based ion sensing within an optical fiber.

    PubMed

    Englich, Florian V; Foo, Tze Cheung; Richardson, Andrew C; Ebendorff-Heidepriem, Heike; Sumby, Christopher J; Monro, Tanya M

    2011-01-01

    We combine suspended-core microstructured optical fibers with the photoinduced electron transfer (PET) effect to demonstrate a new type of fluorescent optical fiber-dip sensing platform for small volume ion detection. A sensor design based on a simple model PET-fluoroionophore system and small core microstructured optical fiber capable of detecting sodium ions is demonstrated. The performance of the dip sensor operating in a high sodium concentration regime (925 ppm Na(+)) and for lower sodium concentration environments (18.4 ppm Na(+)) is explored and future approaches to improving the sensor's signal stability, sensitivity and selectivity are discussed.

  11. Effect of viscosity on photoinduced electron transfer reaction: An observation of the Marcus inverted region in homogeneous solvents

    NASA Astrophysics Data System (ADS)

    Saini, Rajesh Kumar; Kuchlyan, Jagannath; Sarkar, Nilmoni

    2016-09-01

    The viscosity effect of homogeneous solvents on the dynamics of photoinduced electron transfer (PET) reaction among the coumarins and N,N-dimethylaniline (DMA) is investigated using steady-state and time-resolved fluorescence spectroscopy. A bell shape Marcus inversion in the ET rates has been detected in the plot of ET rate constant (kq) with free energy change (ΔG0) in viscous solvents decanol and EG, but it is not observed in DMSO like low viscous solvent. We have also reported that there is no complex formation between the coumarin dye and DMA molecule by using fluorescence correlation spectroscopy.

  12. Interaction of fluorescence dyes with 5-fluorouracil: A photoinduced electron transfer study in bulk and biologically relevant water

    NASA Astrophysics Data System (ADS)

    Kuchlyan, Jagannath; Banik, Debasis; Kundu, Niloy; Roy, Arpita; Sarkar, Nilmoni

    2014-10-01

    The interactions of widely used chemotherapeutic drug, 5-fluorouracil (5FU) with coumarin dyes have been investigated for the first time using steady-state and time-resolved fluorescence spectroscopic measurements. The fluorescence quenching along with the decrease in lifetimes of excited state of coumarin derivatives with gradual addition of 5FU is explained by photoinduced electron transfer (PET) mechanism. Our studies were performed in bulk water and confined water of AOT (aerosol OT) reverse micelle to investigate the effect of confinement on PET dynamics. The feasibility of PET reaction for coumarin-5FU systems is investigated calculating the standard free energy changes using the Rehm-Weller equation.

  13. Electron spectrometer in adjustable triode configuration for photo-induced field emission measurements

    NASA Astrophysics Data System (ADS)

    Bornmann, B.; Mingels, S.; Dams, F.; Prommesberger, C.; Schreiner, R.; Lützenkirchen-Hecht, D.; Müller, G.

    2012-01-01

    We have constructed a new ultrahigh vacuum apparatus with a triode configuration for the systematic investigation of photo-induced field emission (PFE) from metallic or semiconducting cathodes. These are exposed to electric fields up to 400 MV/m and laser irradiation by means of hole or mesh gates. Cathodes and gates are in situ exchangeable and adjustable with high precision to ensure a homogeneous extraction of electrons which are partially transmitted to the fixed electron spectrometer. Its hemispherical sector analyzer provides an energy resolution limit of 8 meV. The commissioning of the measurement system has been performed with a tungsten needle. Its temperature showed up in the high-energy tail of the electron spectrum, while its work function was derived from the spectral low-energy part combined with the integral current-voltage curve. First PFE measurements on B-doped Si-tip arrays yielded a small field emission current increase under green laser illumination. A shift and splitting of the energy spectra was observed which revealed different emission regimes as well as the photosensitivity of the cathode due to carrier excitation into the conduction band. For the full exploitation of the PFE system, a tunable laser over a wide eV-range is required.

  14. Electron spectrometer in adjustable triode configuration for photo-induced field emission measurements

    SciTech Connect

    Bornmann, B.; Mingels, S.; Luetzenkirchen-Hecht, D.; Mueller, G.; Dams, F.; Prommesberger, C.; Schreiner, R.

    2012-01-15

    We have constructed a new ultrahigh vacuum apparatus with a triode configuration for the systematic investigation of photo-induced field emission (PFE) from metallic or semiconducting cathodes. These are exposed to electric fields up to 400 MV/m and laser irradiation by means of hole or mesh gates. Cathodes and gates are in situ exchangeable and adjustable with high precision to ensure a homogeneous extraction of electrons which are partially transmitted to the fixed electron spectrometer. Its hemispherical sector analyzer provides an energy resolution limit of 8 meV. The commissioning of the measurement system has been performed with a tungsten needle. Its temperature showed up in the high-energy tail of the electron spectrum, while its work function was derived from the spectral low-energy part combined with the integral current-voltage curve. First PFE measurements on B-doped Si-tip arrays yielded a small field emission current increase under green laser illumination. A shift and splitting of the energy spectra was observed which revealed different emission regimes as well as the photosensitivity of the cathode due to carrier excitation into the conduction band. For the full exploitation of the PFE system, a tunable laser over a wide eV-range is required.

  15. Photoinduced charge separation at polymer-fullerene interfaces of BHJ solar cells (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Poluektov, Oleg G.; Niklas, Jens; Mardis, Kristy

    2016-09-01

    While photovoltaic cells are highly promising man-made devices for direct solar energy utilization, a number of fundamental questions about how the organic bulk heterojunction cell enables efficient long-lived and long-range charge separation remain unanswered. These questions were address by employing an advanced suite of EPR spectroscopy in combination with DFT calculations to study mechanism of charge separation at the polymer-fullerene interfaces of photo-active BHJ. Observed charge delocalization in BHJ upon photoinduced ET is analogous to that in organic donor-acceptor material. This is an efficient mechanism of charge stabilization in photosynthetic assemblies. Time-resolved EPR spectra show a strong polarization pattern for all polymer-fullerene blends under study, which is caused by non-Boltzmann population of the electron spin energy levels in the radical pairs. The first observation of this phenomenon was reported in natural and artificial photosynthetic assemblies, and comparison with these systems allows us to better understand charge separation processes in OPVs. The spectral analysis presented here, in combination with DFT calculations, shows that CS processes in OPV materials are similar to that in organic photosynthetic systems. This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, under Contract DE-AC02-06CH11357 at Argonne National Laboratory.

  16. Electron spectrometer in adjustable triode configuration for photo-induced field emission measurements.

    PubMed

    Bornmann, B; Mingels, S; Dams, F; Prommesberger, C; Schreiner, R; Lützenkirchen-Hecht, D; Müller, G

    2012-01-01

    We have constructed a new ultrahigh vacuum apparatus with a triode configuration for the systematic investigation of photo-induced field emission (PFE) from metallic or semiconducting cathodes. These are exposed to electric fields up to 400 MV∕m and laser irradiation by means of hole or mesh gates. Cathodes and gates are in situ exchangeable and adjustable with high precision to ensure a homogeneous extraction of electrons which are partially transmitted to the fixed electron spectrometer. Its hemispherical sector analyzer provides an energy resolution limit of 8 meV. The commissioning of the measurement system has been performed with a tungsten needle. Its temperature showed up in the high-energy tail of the electron spectrum, while its work function was derived from the spectral low-energy part combined with the integral current-voltage curve. First PFE measurements on B-doped Si-tip arrays yielded a small field emission current increase under green laser illumination. A shift and splitting of the energy spectra was observed which revealed different emission regimes as well as the photosensitivity of the cathode due to carrier excitation into the conduction band. For the full exploitation of the PFE system, a tunable laser over a wide eV-range is required.

  17. Photoinduced electron transfer and geminate recombination in the group head region of micelles

    NASA Astrophysics Data System (ADS)

    Glusac, Ksenija; Goun, Alexei; Fayer, M. D.

    2006-08-01

    A pump-probe spectroscopic study of photoinduced forward electron transfer and geminate recombination between donors and acceptors located in the head group regions of micelles is presented. The hole donor is octadecyl-rhodamine B (ODRB) and the hole acceptor is N,N-dimethyl-aniline (DMA). The experiments are conducted as a function of the DMA concentration in the dodecyltrimethylammonium bromide and tetradecyltrimethylammonium bromide micelles. In spite of the fact that the absorptions of both the ODRB radical and ground state bleach spectrally overlap with the ODRB excited state absorption, a procedure that makes it possible to determine the geminate recombination dynamics is presented. These experiments are the first to measure the dynamics of geminate recombination in micelles, and the experiments have two orders of magnitude better time resolution than previous studies of forward transfer. The experimental data are compared to statistical mechanics theoretical calculations of both the forward transfer and the geminate recombination. The theory includes important aspects of the topology of the micelle and the diffusion of the donor-acceptors in the micelle head group region. A semiquantitative but nonquantitative agreement between theory and experiments is achieved.

  18. Ultrafast Photoinduced Electron Transfer from Peroxide Dianion.

    PubMed

    Anderson, Bryce L; Maher, Andrew G; Nava, Matthew; Lopez, Nazario; Cummins, Christopher C; Nocera, Daniel G

    2015-06-18

    The encapsulation of peroxide dianion by hexacarboxamide cryptand provides a platform for the study of electron transfer of isolated peroxide anion. Photoinitiated electron transfer (ET) between freely diffusing Ru(bpy)3(2+) and the peroxide dianion occurs with a rate constant of 2.0 × 10(10) M(-1) s(-1). A competing electron transfer quenching pathway is observed within an ion pair. Picosecond transient spectroscopy furnishes a rate constant of 1.1 × 10(10) s(-1) for this first-order process. A driving force dependence for the ET rate within the ion pair using a series of Ru(bpy)3(2+) derivatives allows for the electronic coupling and reorganization energies to be assessed. The ET reaction is nonadiabatic and dominated by a large inner-sphere reorganization energy, in accordance with that expected for the change in bond distance accompanying the conversion of peroxide dianion to superoxide anion.

  19. Photo-Induced Effect on Bacterial Cells

    NASA Astrophysics Data System (ADS)

    El Batanouny, M. H.; Amin, Rehab M.; Naga, M. I.; Ibrahim, M. K.

    2010-04-01

    Bacterial resistance against antibiotics is an increasing problem in medicine. This stimulates study of other bactericidal regimens, one of which is photodynamic therapy (PDT), which involves the killing of bacterial species by low power laser light (LLL) in the presence of photosensitizing agent. It has already been shown that, various gram- negative and gram-positive bacteria can be killed by photodynamic therapy in vitro, using exogenous sensitizers. The mechanisms of laser action on bacteria are not adequately understood. Here, PDT on H. pylori, as an example of gram negative bacteria was studied. The ultra structure changes of the organism after PDT were examined under electron microscope. Neither Irradiation with laser without sensitizer nor sensitizing without laser has any lethal effect on bacterial cells. However, the successful lethal photosensitization was achieved by applying certain laser dose with the corresponding concentration of the photosensitizer. On the other hand, PDT has no significant effect on the genomic DNA of the cells.

  20. Climate Change to the Nuclear Fuel Cycle: Expanding the spectral (14)CO(2) database for non-AMS Field Measurement Systems

    NASA Astrophysics Data System (ADS)

    Marino, B. D. V.; Odonnell, R. G.; Tolliver, D. E.

    2014-06-01

    Accelerator Mass Spectrometry (AMS) is well known and universally employed for radiocarbon analysis but is not adaptable to in-situ field measurements limiting applications. 14CO2 is a key tracer for fossil fuel CO2 as well as for release of enriched 14CO2 characteristic of the nuclear fuel cycle with ∆14CO2 values ranging from -1000 to ˜+500 per mil. However, to exploit the full value of in situ 14CO2 data in diverse climate change and nuclear fuel cycle applications, high data rate temporal and spatial field measurement sensors and systems are required. The development of non-AMS methods based on quantum cascade laser, cavity ring down and optogalvanic spectroscopy are emerging applications but not fully developed for field use or widely accepted. Spectral data for lasing transitions for 14CO2 are lacking in contrast to HITRAN data available for 12CO2 (626) and 13CO2 (636) (among other isotopologues 628, 638, etc.) in the spectral databases limiting development and innovation in non-AMS 14CO2 sensors and systems. We review the corpus of 14CO2 spectral data available in the literature and document grating tuned isotopic lasers (e.g., Freed 19901; Bradley et al., 19862), well suited for expanded spectral studies of 14CO2 and inclusion in the HITRAN database. Non-AMS 14CO2 approaches are reviewed with suggestions for future work to support field systems for 14CO2 measurements. Available isotopic lasers for 14CO2 collaborative studies are described.

  1. Monitoring of drug and stimulation induced cerebral blood flow velocity changes in rat sensory cortex using spectral domain Doppler optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Wang, Chuan; Yang, Yong; Ding, Zhihua; Meng, Jie; Wang, Kai; Yang, Wenwei; Xu, Ying

    2011-04-01

    Doppler optical coherence tomography (DOCT) provides a novel method to measure blood flow velocity in vessels with diameter at micrometer scale. In this study, a developed spectral domain DOCT system is applied to monitor cerebral blood flow velocity changes in a rat. An animal model with a cranial window is used, and by application of a drug, light, and electric stimulations, changes in blood flow velocity of the pial artery in sensory cortex are measured in real time. The results show significant differences in blood flow velocity before and after drug administration or light and electric stimulations, demonstrating the feasibility of DOCT in cerebral microcirculation study. Given its noninvasive nature, high spatial resolution, high velocity sensitivity, and high imaging speed, DOCT shows great promise in brain research by imaging blood flow changes at micrometer scale vessels, which helps to understand the pathogenesis of cerebral diseases and neurodegenerative diseases.

  2. Photoinduced aging and viscosity evolution in Se-rich Ge-Se glasses

    SciTech Connect

    Gueguen, Yann; Sangleboeuf, Jean-Christophe; Rouxel, Tanguy; King, Ellyn A.; Lucas, Pierre; Keryvin, Vincent; Bureau, Bruno

    2013-08-21

    We propose here to investigate the non-equilibrium viscosity of Ge-Se glasses under and after light irradiation. Ge{sub 10}Se{sub 90} and Ge{sub 20}Se{sub 80} fibers have been aged in the dark and under ambient light, over months. During aging, both the relaxation of enthalpy and the viscosity have been investigated. The viscosity was measured by shear relaxation-recovery tests allowing the measurement of non-equilibrium viscosity. When Ge{sub 10}Se{sub 90} glass fibers are aged under irradiation, a relatively fast fictive temperature decrease is observed. Concomitantly, during aging under irradiation, the non-equilibrium viscosity increases and reaches an equilibrium after two months of aging. This viscosity increase is also observed in Ge{sub 20}Se{sub 80} fibers. Nevertheless, this equilibrium viscosity is far below the viscosity expected at the configurational equilibrium. As soon as the irradiation ceases, the viscosity increases almost instantaneously by about one order of magnitude. Then, if the fibers are kept in the dark, their viscosity slowly increases over months. The analysis of the shear relaxation functions shows that the aging is thermorheologically simple. On the other side, there is no simple relaxation between the shear relaxation functions measured under irradiation and those measured in the dark. These results clearly suggest that a very specific photoinduced aging process occurs under irradiation. This aging is due to photorelaxation. Nevertheless, the viscosity changes are not solely correlated to photoaging and photorelaxation. A scenario is proposed to explain all the observed viscosity evolutions under and after irradiation, on the basis of photoinduced transient defects.

  3. Dynamics of photoinduced reactions at oxide surfaces

    NASA Astrophysics Data System (ADS)

    Al-Shamery, K.

    1996-11-01

    This report summarizes our work on UV-laser induced desorption of small molecules and atoms from transition metal oxides. The systems presented serve as examples for a simple photochemical reaction, the fission of the molecule surface bond. State resolved detection methods were used to record the final state distributions of the desorbing neutral molecules. Detailed results on the systems NO/NiO(1 1 1) and CO/Cr2O3(0 0 0 1) are presented. The experiments include investigations on stereodynamic aspects like the angular distributions of the desorbing molecules and, in the case of CO desorption, the rotational alignment with respect to the surface normal. Large desorption cross sections of (6±1) ṡ 10-17 cm2 for NO and (3.5±1) ṡ 10-17 cm2 for CO have been found for the desorption at 6.4 eV. The wavelength dependence indicates that the primary excitation step is substrate induced. The final state distributions show a high degree of translational, rotational and vibrational excitation and are clearly nonthermal of origin. The results are consistent with the formation of a negative ion intermediate state of the adsorbate. This observation is supported from a comparison to former results on NO/NiO(1 0 0) for which extensive ab initio calculations including electronically excited states exist. A spin state dependence of the vibrational excitation of NO could only be observed for NO/NiO(1 1 1) and is absent for NO/NiO(1 0 0). We attribute this observation to a spin state dependent coupling of the desorbing molecule to the surface in case the spin lattice orientation of the surface shows a preferential orientation. In the (1 1 1) plane the spin orientation is parallel within neighbour nickel ions while it is alternating in the (1 0 0) plane. For both systems studied the velocity component parallel to the surface is constant leading to a strong peaking along the surface normal for the fast molecules. The change from a preferred helicopter rotation (angular momentum

  4. Photo-induced Mass Transport through Polymer Networks

    NASA Astrophysics Data System (ADS)

    Meng, Yuan; Anthamatten, Mitchell

    2014-03-01

    Among adaptable materials, photo-responsive polymers are especially attractive as they allow for spatiotemporal stimuli and response. We have recently developed a macromolecular network capable of photo-induced mass transport of covalently bound species. The system comprises of crosslinked chains that form an elastic network and photosensitive fluorescent arms that become mobile upon irradiation. We form loosely crosslinked polymer networks by Michael-Addition between multifunctional thiols and small molecule containing acrylate end-groups. The arms are connected to the network by allyl sulfide, that undergoes addition-fragmentation chain transfer (AFCT) in the presence of free radicals, releasing diffusible fluorophore. The networks are loaded with photoinitiator to allow for spatial modulation of the AFCT reactions. FRAP experiments within bulk elastomers are conducted to establish correlations between the fluorophore's diffusion coefficient and experimental variables such as network architecture, temperature and UV intensity. Photo-induced mass transport between two contacted films is demonstrated, and release of fluorophore into a solvent is investigated. Spatial and temporal control of mass transport could benefit drug release, printing, and sensing applications.

  5. Model for photoinduced bending of slender molecular crystals.

    PubMed

    Nath, Naba K; Pejov, Ljupčo; Nichols, Shane M; Hu, Chunhua; Saleh, Na'il; Kahr, Bart; Naumov, Panče

    2014-02-19

    The growing realization that photoinduced bending of slender photoreactive single crystals is surprisingly common has inspired researchers to control crystal motility for actuation. However, new mechanically responsive crystals are reported at a greater rate than their quantitative photophysical characterization; a quantitative identification of measurable parameters and molecular-scale factors that determine the mechanical response has yet to be established. Herein, a simple mathematical description of the quasi-static and time-dependent photoinduced bending of macroscopic single crystals is provided. This kinetic model goes beyond the approximate treatment of a bending crystal as a simple composite bilayer. It includes alternative pathways for excited-state decay and provides a more accurate description of the bending by accounting for the spatial gradient in the product/reactant ratio. A new crystal form (space group P21/n) of the photoresponsive azo-dye Disperse Red 1 (DR1) is analyzed within the constraints of the aforementioned model. The crystal bending kinetics depends on intrinsic factors (crystal size) and external factors (excitation time, direction, and intensity).

  6. Photo-induced reduction of flavin mononucleotide in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Song, S.-H.; Dick, B.; Penzkofer, A.

    2007-01-01

    The photo-induced reduction of flavin mononucleotide (FMN) in aqueous solutions is studied by absorption spectra measurement under aerobic and anaerobic conditions. Samples without exogenous reducing agent and with the exogenous reducing agents ethylene-diamine-tetraacetic acid (EDTA) and dithiothreitol (DTT) are investigated. Under anaerobic conditions the photo-induced reduction with and without reducing agents is irreversible. Under aerobic conditions the photo-reduction without added reducing agent is small compared to the photo-degradation, and the photo-reduction of FMN by the reducing agents is reversible (re-oxidation in the dark). During photo-excitation of FMN the dissolved oxygen is consumed by singlet oxygen formation and subsequent chemical reaction. After light switch-off slow re-oxidation (slow absorption recovery) occurs due to air in-diffusion from surface. EDTA degradation by FMN excitation leads to oxygen scavenging. The quantum efficiencies of photo-reduction under aerobic and anaerobic conditions are determined. The re-oxidation of reduced FMN under aerobic conditions and due to air injection is investigated.

  7. Photoinduced development of antibacterial materials derived from isosorbide moiety.

    PubMed

    Lorenzini, Cedric; Haider, Adnan; Kang, Inn-Kyu; Sangermano, Marco; Abbad-Andalloussi, Samir; Mazeran, Pierre-Emmanuel; Lalevée, Jacques; Renard, Estelle; Langlois, Valérie; Versace, Davy-Louis

    2015-03-09

    A straightforward method for immobilizing in situ generated silver nanoparticles on the surface of a photoactivable isosorbide-derived monomer is developed with the objective to design a functional material having antibacterial properties. The photoinduced thiol-ene mechanism involved in these syntheses is described by the electron spin resonance/spin trapping technique. The resulting materials with or without silver nanoparticles (Ag NPs) were used as films or as coatings on glass substrate. The surface of the synthesized materials was characterized by X-ray photoelectron spectroscopy and scanning electron microscopy, and their thermal and mechanical properties were evaluated by dynamic-mechanical thermal tests, differential scanning calorimetry, thermogravimetric analyses, along with pencil hardness, nanoindentation, and scratch resistance tests. The photoinduced formation of Ag NPs is also confirmed by UV spectrophotometry. Finally, a primary investigation demonstrates the antibacterial properties of the isosorbide-derived material against Staphylococcus aureus and Escherichia coli, as well as its cytocompatibility toward NIH 3T3 fibroblastic cells.

  8. Photoinduced giant magnetic polarons in EuTe

    NASA Astrophysics Data System (ADS)

    Henriques, A. B.; Naupa, A. R.; Usachev, P. A.; Pavlov, V. V.; Rappl, P. H. O.; Abramof, E.

    2017-01-01

    Photoinduced magnetic polarons in EuTe, with a magnetic moment of several hundred Bohr magnetons, were investigated as a function of pump intensity and temperature by pump-probe Faraday rotation. The quantum efficiency for optical generation of magnetic polarons is found to be 0.09. The pump-intensity dependence of the photoinduced Faraday rotation shows a sublinear increase, from which we deduce that the population of photoexcited polarons is limited by a maximum value of 4.5 ×1015cm-3 . This is four orders of magnitude less than the concentration of polarons that would completely fill the crystal, which suggests that the photoexcited polarons are anchored by defects. In addition to the generation of polarons, at high pump densities the modulated pump light also causes a small alternating heating of the illuminated region. The temperature dependence of the polaron magnetic moment is well described by the Curie-Weiss law. Above 100 K, polarons are thermally quenched with an activation energy of 11 meV.

  9. Photoinduced Kondo effect in CeZn3P3

    NASA Astrophysics Data System (ADS)

    Kitagawa, J.; Kitajima, D.; Shimokawa, K.; Takaki, H.

    2016-01-01

    The Kondo effect, which originates from the screening of a localized magnetic moment by a spin-spin interaction, is widely observed in nonartificial magnetic materials, artificial quantum dots, and carbon nanotubes. In devices based on quantum dots or carbon nanotubes that target quantum information applications, the Kondo effect can be tuned by a gate voltage, a magnetic field, or light. However, the manipulation of the Kondo effect in nonartificial materials has not been thoroughly studied; in particular, the artificial creation of the Kondo effect remains unexplored. Per this subject study, however, a route for the optical creation of the Kondo effect in the nonartificial material p -type semiconductor CeZn3P3 is presented. The Kondo effect emerges under visible-light illumination of the material by a continuous-wave laser diode and is ultimately revealed by photoinduced electrical resistivity, which clearly exhibits a logarithmic temperature dependency. By contrast, a La-based compound (LaZn3P3 ) displays only normal metallic behavior under similar illumination. The photoinduced Kondo effect, which occurs at higher temperatures when compared with the Kondo effect in artificial systems, provides a potential range of operation for not only quantum information/computation devices but also for operation of magneto-optic devices, thereby expanding the range of device applications based on the Kondo effect.

  10. Millisecond Photoinduced Absorption Studies of Pyridine-Based Copolymer Films

    NASA Astrophysics Data System (ADS)

    Coplin, K. A.; Clark, D. T.; Jessen, S. W.; Epstein, A. J.; Fu, D.-K.; Swager, T. M.

    1997-03-01

    We present a study of the photoexcited states in copolymers of poly(p-pyridyl vinylene) and poly(p-phenylene vinylene) (PPyVPR_iV) with sidegroups R_1=C_12H_25 or R_2=COOC_12H_25 attached at the 2 and 5 positions of the phenyl ring. Previous studies discussed the millisecond photoinduced absorption (ms PA) characteristics of PPyVPR_iV powders(S.W. Jessen et al.), Synth. Met., in press.. In particular, triplet-triplet (T-T) transitions were observed at 1.6 eV for both materials. Additional polaron signatures were also observed in both the electronic ( ~ 0.85 eV) and infrared (1100 - 1600 cm-1) regions of the photoinduced spectrum. We compare these powder results with ms PA features for film morphologies of both the copolymers. We observe a weaker ( ~ 10X) T-T^* transition for copolymer films cast from xylene solution indicating a reduction in triplet exciton production as compared to powder samples. These results are contrasted with the behavior we reported(S.W. Jessen et al.), to be published. earlier for film and powder samples of the parent polymer poly(p-pyridyl vinylene).

  11. Short- and long-term variability of spectral solar UV irradiance at Thessaloniki, Greece: effects of changes in aerosols, total ozone and clouds

    NASA Astrophysics Data System (ADS)

    Fountoulakis, I.; Bais, A. F.; Fragkos, K.; Meleti, C.; Tourpali, K.; Zempila, M. M.

    2015-12-01

    In this study, we discuss the short- and the long-term variability of spectral UV irradiance at Thessaloniki, Greece using a long, quality-controlled data set from two Brewer spectrophotometers. Long-term changes in spectral UV irradiance at 307.5, 324 and 350 nm for the period 1994-2014 are presented for different solar zenith angles and discussed in association to changes in total ozone column (TOC), aerosol optical depth (AOD) and cloudiness observed in the same period. Positive changes in annual mean anomalies of UV irradiance, ranging from 2 to 6 % per decade, have been detected both for clear- and all-sky conditions. The changes are generally greater for larger solar zenith angles and for shorter wavelengths. For clear skies, these changes are, in most cases, statistically significant at the 95 % confidence limit. Decreases in the aerosol load and weakening of the attenuation by clouds lead to increases in UV irradiance in the summer, of 7-9 % per decade for 64° solar zenith angle. The increasing TOC in winter counteracts the effect of decreasing AOD for this particular season, leading to small, statistically insignificant, negative long-term changes in irradiance at 307.5 nm. Annual mean UV irradiance levels are increasing from 1994 to 2006 and remain relatively stable thereafter, possibly due to the combined changes in the amount and optical properties of aerosols. However, no statistically significant corresponding turning point has been detected in the long-term changes of AOD. Trends in irradiance during the two sub-periods are not discussed, because the length of the two datasets is too short for deriving statistically significant estimates. The absence of signatures of changes in AOD in the short-term variability of irradiance in the UV-A may have been caused by changes in the single scattering albedo of aerosols, which may counteract the effects of changes in AOD on irradiance. The anti-correlation between the year-to-year variability of the

  12. Light-Induced Spectral Absorbance Changes in Relation to Photosynthesis and the Epoxidation State of Xanthophyll Cycle Components in Cotton Leaves 1

    PubMed Central

    Bilger, Wolfgang; Björkman, Olle; Thayer, Susan S.

    1989-01-01

    When cotton (Gossypium hirsutum L., cv Acaia SJC-1) leaves kept in weak light were suddenly exposed to strong red actinic light a spectral absorbance change took place having the following prominent characteristics. (a) It was irreversible within the first four minute period after darkening. (b) The difference in leaf absorbance between illuminated and predarkened leaves had a major peak at 505 nanometers, a minor peak at 465 nanometers, a shoulder around 515 nanometers, and minor troughs at 455 and 480 nanometers. (c) On the basis of its spectral and kinetic characteristics this absorbance change can be readily distinguished from the much faster electrochromic shift which has a peak at 515 nanometers, from the slow, so-called light-scattering change which has a broad peak centered around 535 nanometers and is reversed upon darkening, and from absorbance changes associated with light-induced chloroplast rearrangements. (d) The extent and time course of this absorbance change closely matched that of the deepoxidation of violaxanthin to zeaxanthin in the same leaves. (e) Both the absorbance change and the ability to form zeaxanthin were completely blocked in leaves to which dithiothreitol (DTT) had been provided through the cut petlole. DTT treatment also caused strong inhibition of that component of the 535-nanometer absorbance change which is reversed in less than 4 minutes upon darkening and considered to be caused by increased light scattering. Moreover, DTT inhibited a large part of nonphotochemical quenching of chlorophyll fluorescence in the presence of excessive light. However, DTT had no detectable effect on the photon yield of photosynthesis measured under strictly rate-limiting photon flux densities or on the light-saturated photosynthetic capacity, at least in the short term. We conclude that it is possible to monitor light-induced violaxanthin de-epoxidation in green intact leaves by measurement of the absorbance change at 505 nanometers. Determination

  13. Change in the activity character of the coronae of low-mass stars of various spectral types

    NASA Astrophysics Data System (ADS)

    Nizamov, B. A.; Katsova, M. M.; Livshits, M. A.

    2017-03-01

    We study the dependence of the coronal activity index on the stellar rotation velocity. This question has been considered previously for 824 late-type stars on the basis of a consolidated catalogue of soft X-ray fluxes. We carry out a more refined analysis separately for G, K, and M dwarfs. Two modes of activity are clearly identified in them. The first is the saturation mode, is characteristic of young stars, and is virtually independent of their rotation. The second refers to the solar-type activity whose level strongly depends on the rotation period. We show that the transition from one mode to the other occurs at rotation periods of 1.1, 3.3, and 7.2 days for stars of spectral types G2, K4, and M3, respectively. In light of the discovery of superflares on G and K stars from the Kepler spacecraft, the question arises as to what distinguishes these objects from the remaining active late-type stars. We analyze the positions of superflare stars relative to the remaining stars observed by Kepler on the "amplitude of rotational brightness modulation (ARM)—rotation period" diagram. The ARM reflects the relative spots area on a star and characterizes the activity level in the entire atmosphere. G and K superflare stars are shown to be basically rapidly rotating young objects, but some of them belong to the stars with the solar type of activity.

  14. Collision Induced Velocity Changes from Molecular Dynamic Simulations. Application to the Spectral Shape of the Q(1) Raman Lines of H{_2}/H{_2}

    NASA Astrophysics Data System (ADS)

    Tran, H.; Hartmann, J. M.

    2011-06-01

    Collision induced velocity changes for pure H{_2} have been computed from classical dynamic simulations. The results have been compared with the Keilson-Storer model from four different points of view. The first involves various autocorrelation functions associated with the velocity. The second and third give more detailed information, and are time evolutions of some conditional probabilities for changes of the velocity modulus and orientation and the collision kernels themselves. The fourth considers the evolutions, with density, of the half widths of the Q(1) lines of the isotropic Raman (1-0) fundamental band and of the (2-0) overtone quadrupole band. These spectroscopic data enable an indirect test of the models since velocity changes translate into line-shape modifications through the speed dependence of collisional parameters and the Dicke narrowing of the Doppler contribution to the profile. The results indicate that, while the KS approach gives a poor description of detailed velocity-to-velocty changes, it leads to accurate results for the correlation functions and spectral shapes, quantities related to large averages over the velocity. It is also shown that the use of collision kernels directly derived from MDS lead to an almost perfect prediction of all considered quantities (correlation functions, conditional probabilities, and spectral shapes). Finally, the results stress the need for very accurate calculations of line-broadening and -shifting coefficients from the intermolecular potential to obviate the need for experimental data and permit fully meaningful tests of the models. H. Tran, J.M. Hartmann J. Chem. Phys. 130, 094301, 2009.

  15. Anisotropic photo-induced magnetism of a Rb_jCo_k[Fe(CN)_6]_l\\cdotnH_2O thin film

    NASA Astrophysics Data System (ADS)

    Park, J.-H.; Čižmár, E.; Meisel, M. W.; Frye, F.; Lane, S.; Huh, Y. D.; Talham, D. R.

    2004-11-01

    A magneto-optically active thin film of Rb_jCo_k[Fe(CN)_6]_l\\cdotnH_2O has been prepared using a sequential assembly method^a. Upon irradiation with light and at 5 K, the net magnetization of the film increased when the surface of the film was oriented parallel to the external magnetic field of 0.1 T. However, when the surface of the film was perpendicular to the field, the net magnetization phdecreased upon irradiation. The presence of dipolar fields and the low-dimensional nature of the system are used to describe the orientation dependence of the photo-induced magnetization. The ability to increase or decrease the photo-induced magnetization by changing the orientation of the system with respect to the field is a new phenomenon that may be useful in future device applications. ^aJ.-H. Park phet al., preprint, arXiv:cond-mat/0406173.

  16. Persistent photoinduced modifications in the phase-separated states of L a2 -2 xS r1 +2 xM n2O7

    NASA Astrophysics Data System (ADS)

    Sun, Kai; Sun, Shuaishuai; Li, Xingyuan; Li, Zhongwen; Zhang, Ruixin; Wei, Linlin; Guo, Cong; Zheng, Dingguo; Tian, Huanfang; Yang, Huaixin; Li, Jianqi

    2016-11-01

    Reentrant charge-ordering transition (RCOT) in the bilayered perovskite manganite L a2 -2 xS r1 +2 xM n2O7 can yield observable changes in both the structural and physical properties associated with phase separation. Our recent measurements show that laser illumination can result in persistent modifications of both the resistance and microstructure in the phase-separated (PS) states. Measurements of photoinduced effects on an x =0.6 sample reveal a persistent increase of the resistance by as much as 40%. Low-temperature laser in situ transmission electron microscope observations clearly show that in situ laser irradiation can modify the PS nature and strengthen the charge-ordered state. We attribute these photoinduced phenomena to the optical modulation of the hole concentration in the Mn O2 layers and the alteration of the local Mn orbital configurations in the PS states.

  17. Photoinduced currents in pristine and ion irradiated kapton-H polyimide

    SciTech Connect

    Sharma, Anu Sridharbabu, Y. Quamara, J. K.

    2014-10-15

    The photoinduced currents in pristine and ion irradiated kapton-H polyimide have been investigated for different applied electric fields at 200°C. Particularly the effect of illumination intensity on the maximum current obtained as a result of photoinduced polarization has been studied. Samples were irradiated by using PELLETRON facility, IUAC, New Delhi. The photo-carrier charge generation depends directly on intensity of illumination. The samples irradiated at higher fluence show a decrease in the peak current with intensity of illumination. The secondary radiation induced crystallinity (SRIC) is responsible for the increase in maximum photoinduced currents generated with intensity of illumination.

  18. Pressure-induced spectral changes for the special-pair radical cation of the bacterial photosynthetic reaction center.

    PubMed

    Leiger, Kristjan; Freiberg, Arvi; Dahlbom, Mats G; Hush, Noel S; Reimers, Jeffrey R

    2007-06-07

    The effect of pressure up to 6 kbars on the near to mid infrared absorption spectrum (7500-14,300 cm(-1) or 1333-700 nm) of the oxidized reaction center of Rhodobacter sphaeroides is measured and interpreted using density-functional B3LYP, INDO, and PM5 calculations. Two weak electronic transition origins at approximately 8010 and approximately 10,210 cm(-1) are unambiguously identified. The first transition is assigned to a Qy tripdoublet band that involves, in the localized description of the excitation, a triplet absorption on one of the bacteriochlorophyll molecules (PM) in the reaction center's special pair intensified by the presence of a radical cation on the other (PL). While most chlorophyll transition energies decrease significantly with increasing pressure, the tripdoublet band is found to be almost pressure insensitive. This difference is attributed to the additional increase in the tripdoublet-band energy accompanying compression of the pi-stacked special pair. The second band could either be the anticipated second Qy tripdoublet state, a Qx tripdoublet state, or a state involving excitation from a low-lying doubly occupied orbital to the half-occupied cationic orbital. A variety of absorption bands that are also resolved in the 8300-9600 cm(-1) region are assigned as vibrational structure associated with the first tripdoublet absorption. These sidebands are composites that are shown by the calculations to comprise many unresolved individual modes; while the calculated pressure sensitivity of each individual mode is small, the calculated pressure dependence of the combined sideband structure is qualitatively similar to the observed pressure dependence, preventing the positive identification of possible additional electronic transitions in this spectral region.

  19. Enhancement of Photoinduced Charge-Order Melting via Anisotropy Control by Double-Pulse Excitation in Perovskite Manganites: Pr_{0.6}Ca_{0.4}MnO_{3}.

    PubMed

    Yada, H; Ijiri, Y; Uemura, H; Tomioka, Y; Okamoto, H

    2016-02-19

    To control the efficiency of photoinduced charge-order melting in perovskite manganites, we performed femtosecond pump-probe spectroscopy using double-pulse excitation on Pr_{0.6}Ca_{0.4}MnO_{3}. The results revealed that the transfer of the spectral weight from the near-infrared to infrared region by the second pump pulse is considerably enhanced by the first pump pulse and that the suppression of crystal anisotropy, that is, the decrease of long-range lattice deformations due to the charge order by the first pump pulse is a key factor to enhance the charge-order melting. This double-pulse excitation method can be applied to various photoinduced transitions in complex materials with electronic and structural instabilities.

  20. Photoinduced Acrylate Polymerization: Unexpected Reduction in Chain Branching.

    PubMed

    Wenn, Benjamin; Reekmans, Gunter; Adriaensens, Peter; Junkers, Thomas

    2015-08-01

    The branching stemming from midchain radical formation in n-butyl acrylate polymerization is investigated via melt-state (13) C NMR measurements. The dependence of the degree of branching (DB) on the monomer conversion of the system is examined for photoinduced polymerizations, revealing a steady increase in branching with conversion. For polymerization at moderate light intensities, an increase in branching from 0.03% to 0.37% is observed for polymerizations at 60 °C, which is fivefold below the level of branching observed in thermally initiated polymerizations under otherwise identical reaction conditions. The reason for this overall reduction in branching remains momentarily unclear; yet, a strong dependence of branching on light intensity is observed. While polymerization under a 1 W LED lamp results at almost full monomer conversion in branching degrees of 0.22%, polymerization under a 400 W lamp yields 1.81% of chain branches.

  1. Photoinduced charge transfer phase transition in cesium manganese hexacyanoferrate

    SciTech Connect

    Matsuda, Tomoyuki; Tokoro, Hiroko; Hashimoto, Kazuhito; Ohkoshi, Shin-ichi

    2007-05-01

    Cesium manganese hexacyanoferrate, Cs{sub 1.51}Mn[Fe(CN){sub 6}], shows a thermal phase transition between Mn{sup II}-NC-Fe{sup III} [high-temperature (HT) phase] and Mn{sup III}-NC-Fe{sup II} [low-temperature (LT) phase] with phase transition temperatures of 170 K (HT{yields}LT) and 230 K (LT{yields}HT). The LT phase shows ferromagnetism with Curie temperature of 7 K and coercive field of 60 Oe. Irradiating with 532 nm laser light converts the LT phase into the photoinduced (PI) phase, which does not have spontaneous magnetization. The electronic state of the PI phase corresponds to that of the HT phase and the relaxation temperature from the PI to the LT phase is observed at 90 K.

  2. Photoinduced surface voltage mapping study for large perovskite single crystals

    NASA Astrophysics Data System (ADS)

    Liu, Xiaojing; Liu, Yucheng; Gao, Fei; Yang, Zhou; Liu, Shengzhong Frank

    2016-05-01

    Using a series of illumination sources, including white light (tungsten-halogen lamp), 445-nm, 532-nm, 635-nm, and 730-nm lasers, the surface photovoltage (SPV) images were mapped for centimeter-sized CH3NH3PbX3 (X = Cl, Br, I) perovskite single crystals using Kelvin probe force microscopy. The significant SPV signals were observed to be wavelength-dependent. We attribute the appreciable SPV to the built-in electric field in the space charge region. This study shines light into the understanding of photoinduced charge generation and separation processes at nanoscale to help advance the development of perovskite solar cells, optoelectronics, laser, photodetector, and light-emitting diode (LED).

  3. Photoinduced Magnetization in a Thin Fe-CN-Co Film.

    NASA Astrophysics Data System (ADS)

    Huh, Y. D.; Talham, D. R.; Park, J.-H.; Meisel, M. W.

    2004-03-01

    We have studied the photoinduced magnetization of a new low dimensional system, a thin film of a Prussian blue derivative, Rb_jCo_k[Fe(CN)_6]_l. This film was synthesized by the sequential depositions of Rb^+/Co^2+ and [Fe(CN)_6]^3- ions on the surface of a templated Fe-CN-Co monolayer. In this novel 2D system, high spin states of the Fe and Co spins interact antiferromagnetically and experience long range ordering below 20 K. The spins form domains that exhibit behavior consistent with a cluster spin-glass description. Upon illumination with light, the population of the high spin states increases, resulting in a rapid increase of the magnetization of the film and a modification of the cluster spin-glass properties.

  4. DNA Intercalated Psoralen Undergoes Efficient Photoinduced Electron Transfer.

    PubMed

    Fröbel, Sascha; Reiffers, Anna; Torres Ziegenbein, Christian; Gilch, Peter

    2015-04-02

    The interaction of psoralens with DNA has been used for therapeutic and research purposes for decades. Still the photoinduced behavior of psoralens in DNA has never been observed directly. Femtosecond transient absorption spectroscopy is used here to gain direct insight into the photophysics of a DNA-intercalated psoralen (4'-aminomethyl-4,5',8-trimethyl-psoralen (AMT)). Intercalation reduces the excited singlet lifetime of AMT to 4 ps compared with 1400 ps for AMT in water. This singlet quenching prohibits the population of the triplet state that is accessed in free AMT. Instead, a DNA to AMT electron transfer takes place. The resulting radical pair decays primarily via charge recombination with a time constant of 30 ps. The efficient electron transfer observed here reveals a completely new aspect of the psoralen-DNA interaction.

  5. Method for characterizing bulk recombination using photoinduced absorption

    NASA Astrophysics Data System (ADS)

    Wilson, Nora M.; Sandén, Simon; Sandberg, Oskar J.; Österbacka, Ronald

    2017-03-01

    The influence of reaction order and trap-assisted recombination on continuous-wave photoinduced absorption measurements is clarified through analytical calculations and numerical simulations. The results reveal the characteristic influence of different trap distributions and enable distinguishing between shallow exponential and Gaussian distributions and systems dominated by direct recombination by analyzing the temperature dependence of the in-phase and quadrature signals. The identifying features are the intensity dependence of the in-phase at high intensity, P A I ∝ I γ HI , and the frequency dependence of the quadrature at low frequency, P A Q ∝ ω γ LF . For direct recombination, γHI and γLF are temperature independent, and for an exponential distribution, they depend on the characteristic energy Ech as γ HI = 1 / ( 1 + E ch / k T ) and γ LF = k T / E ch , while a Gaussian distribution shows γHI and γLF as functions of I and ω, respectively.

  6. Photo-induced reflectivity in the mid and far infrared

    SciTech Connect

    Haar, P.; Harrington, K.J.; Schwettman, H.A.

    1995-12-31

    Interest in switching FEL beams has motivated studies of photo-induced reflectivity in the mid and far infrared. We are particularly interested in Ge{sup 4}, GaAs, and Si{sup 5}, materials that can be pumped with a visible or near-IR conventional laser and which together cover the wavelengths from 3-100{mu}m. We have made quantitative measurements to determine the induced reflectivity, carrier lifetime, and transient absorption of these materials at several wavelengths across this range using a variety of pump laser wavelengths and pulse lengths. These measurements allow us to determine the feasibility of single pulse selection and cavity dumping with our FELs at high repetition rates.

  7. Photoinduced electron transfer between benzyloxy dendrimer phthalocyanine and benzoquinone

    NASA Astrophysics Data System (ADS)

    Zhang, Tiantian; Ma, Dongdong; Pan, Sujuan; Wu, Shijun; Jiang, Yufeng; Zeng, Di; Yang, Hongqin; Peng, Yiru

    2016-10-01

    Photo-induced electron transfer (PET) is an important and fundamental process in natural photosynthesis. To mimic such interesting PET process, a suitable donor and acceptor couple were properly chosen. Dendrimer phthalocyanines and their derivatives have emerged as promising materials for artificial photosynthesis systems. In this paper, the electron transfer between the light harvest dendrimer phthalocyanine (donor) and the 1,4-benzoquinone (acceptor) was studied by UV/Vis and fluorescence spectroscopic methods. It was found that fluorescence of phthalocyanine was quenched by benzoquinone (BQ) via excited state electron transfer, from the phthalocyanine to the BQ upon excitation at 610 nm. The Stern-Volmer constant (KSV) of electron transfer was calculated. Our study suggests that this dendritic phthalocyanine is an effective new electron donor and transmission complex and could be used as a potential artificial photosynthesis system.

  8. Luminescence and photoinduced absorption in ytterbium-doped optical fibres

    SciTech Connect

    Rybaltovsky, A A; Aleshkina, S S; Likhachev, M E; Bubnov, M M; Umnikov, A A; Yashkov, M V; Gur'yanov, Aleksei N; Dianov, Evgenii M

    2011-12-31

    Photochemical reactions induced in the glass network of an ytterbium-doped fibre core by IR laser pumping and UV irradiation have been investigated by analysing absorption and luminescence spectra. We have performed comparative studies of the photoinduced absorption and luminescence spectra of fibre preforms differing in core glass composition: Al{sub 2}O{sub 3} : SiO{sub 2}, Al{sub 2}O{sub 3} : Yb{sub 2}O{sub 3} : SiO{sub 2}, and P{sub 2}O{sub 5} : Yb{sub 2}O{sub 3} : SiO{sub 2}. The UV absorption spectra of unirradiated preform core samples show strong bands peaking at 5.1 and 6.5 eV, whose excitation plays a key role in photoinduced colour centre generation in the glass network. 'Direct' UV excitation of the 5.1- and 6.5-eV absorption bands at 244 and 193 nm leads to the reduction of some of the Yb{sup 3+} ions to Yb{sup 2+}. The photodarkening of ytterbium-doped fibres by IR pumping is shown to result from oxygen hole centre generation. A phenomenological model is proposed for the IR-pumping-induced photodarkening of ytterbium-doped fibres. The model predicts that colour centre generation in the core glass network and the associated absorption in the visible range result from a cooperative effect involving simultaneous excitation of a cluster composed of several closely spaced Yb{sup 3+} ions.

  9. Photoinduced properties of nanocrystalline TiO2-anatase coating on Ti-based bone implants.

    PubMed

    Lorenzetti, Martina; Biglino, Daniele; Novak, Saša; Kobe, Spomenka

    2014-04-01

    The paper reports on the photoinduced properties of hydrothermally treated (HT) titanium used for bone implants. The anatase coatings composed of 30-100nm anatase crystals exhibited high photocatalytic activity and good photo-induced wettability, reaching a superhydrophilic state, despite the larger crystal dimensions than the previously reported optimal ones. These properties are due to a suitable combination of surface texture, roughness, thickness, crystal morphology and particle size, which allowed the two independent photo-induced phenomena to occur simultaneously. The results on caffeine degradation by photocatalysis and the prolonged effect (up to two weeks) of photo-induced wettability in dark suggested a possible applicability of the HT anatase coatings as bacteria-repelling surfaces for body implants, in favor of a better osseointegration in vivo.

  10. Ornaments in radiation treatment of cultural heritage: Color and UV-vis spectral changes in irradiated nacres

    NASA Astrophysics Data System (ADS)

    Marušić, Katarina; Pucić, Irina; Desnica, Vladan

    2016-07-01

    Cultural heritage objects that are radiation treated in order to stop their biodegradation often contain ornamenting materials that cannot be removed. Radiation may produce unwanted changes to such materials. Nacre is a common ornamenting material so this is an attempt to assess the impact of gamma-radiation on its optical properties. Two types of nacre (yellow and white) were obtained from a museum and subjected to different absorbed doses of Co-60 gamma irradiation under the same conditions. The radiation induced changes of nacres color were investigated with fiber optic reflectance spectroscopy (FORS). Colorimetry in CIE Lab space revealed that in both nacres the lightness shifted to darker grey hues at high doses while the color component's (red, green, yellow and blue) behavior depended on the nacre type. Observable changes occurred at doses much above the dose range needed for radiation treatment of cultural heritage objects that are often ornamented with nacre. In UV-vis reflectance spectra of samples irradiated to high doses carbonate radical anion absorption appeared.

  11. Unintended compositional changes in transgenic rice seeds ( Oryza sativa L.) studied by spectral and chromatographic analysis coupled with chemometrics methods.

    PubMed

    Jiao, Zhe; Si, Xiao-xi; Li, Gong-ke; Zhang, Zhuo-min; Xu, Xin-ping

    2010-02-10

    Unintended compositional changes in transgenic rice seeds were studied by near-infrared reflectance, GC-MS, HPLC, and ICP-AES coupled with chemometrics strategies. Three kinds of transgenic rice with resistance to fungal diseases or insect pests were comparatively studied with the nontransgenic counterparts in terms of key nutrients such as protein, amino acids, fatty acids, vitamins, elements, and antinutrient phytic acid recommended by the Organization for Economic Co-operation and Development (OECD). The compositional profiles were discriminated by chemometrics methods, and the discriminatory compounds were protein, three amino acids, two fatty acids, two vitamins, and several elements. Significance of differences for these compounds was proved by analysis of variance, and the variation extent ranged from 20 to 74% for amino acids, from 19 to 38% for fatty acids, from 25 to 57% for vitamins, from 20 to 50% for elements, and 25% for protein, whereas phytic acid content did not change significantly. The unintended compositional alterations as well as unintended change of physical characteristic in transgenic rice compared with nontransgenic rice might be related to the genetic transformation, the effect of which needs to be elucidated by additional studies.

  12. Irradiance and Temperature Dependence of Photo-Induced Orientation in Two Azobenzene-Based Polymers

    DTIC Science & Technology

    1998-06-23

    and Almeria Natansohn* Department of Chemistry, Queen’s University, Kingston, Ontario, K7L 3N6 Paul Rochon Department of Physics, Royal Military...1. IRRADIANCE AND TEMPERATURE DEPENDENCE OF PHOTO-INDUCED ORIENTATION IN TWO AZOBENZENE-BASED POLYMERS Dennis Hore and Almeria Natansohn...IRRADIANCE AND TEMPERATURE DEPENDENCE OF PHOTO-INDUCED ORIENTATION IN TWO AZOBENZENE-BASED POLYMERS Dennis Hore and Almeria Natansohn Department of

  13. Alternating photoinduced mass transport triggered by light polarization in azobenzene containing sol-gel films

    NASA Astrophysics Data System (ADS)

    Fabbri, F.; Lassailly, Y.; Lahlil, K.; Boilot, J. P.; Peretti, J.

    2010-02-01

    Combined shear-force and near-field optical microscopies are used for real-time monitoring of the formation of photoinduced surface relief gratings in photochromic thin films containing azobenzene derivatives. The correlated optical and topographical images provide evidence that the direction of the photoinduced matter migration is defined by the light polarization pattern and that, for a given light intensity pattern, modulating the polarization between two orthogonal states gives rise to alternating mass transport.

  14. Photoswitchable stable charge-distributed states in a new cobalt complex exhibiting photo-induced valence tautomerism.

    PubMed

    Slota, Michael; Blankenhorn, Marian; Heintze, Eric; Vu, Minh; Hübner, Ralph; Bogani, Lapo

    2015-01-01

    We report the synthesis and magnetic and photomagnetic behaviour of a novel valence tautomeric cobalt complex, [Co(3,5-dbbq)2(μ-bpym)] (1) (3,5-dbbq = 3,5-di-tert-butyl-1,2-benzoquinone and μ-bpym = 2,2'-bipyrimidine). The synthesis is performed by reacting Co2(CO)8 and μ-bpym in the presence of the ligand 3,5-dbbq in a mixed solvent under inert atmosphere. The magnetic behavior clearly shows the presence of electron transfer from the catecholate ligand to the cobalt center, producing valence tautomers of [Co(II)(SQ)2] with a transition temperature (T1/2) of 215 K. Photomagnetic studies, performed via both SQUID magnetometry and X-band electron paramagnetic resonance, show the clear presence of photoinduced valence tautomerism, at temperatures considerably higher than previous systems. A metastable charge distribution is observed, strengthening previous investigations on the character of mixed valence ligands. Entropy-driven valence tautomeric interconversion is observed, and drives the transition to the most stable charge distribution. The complex has the ability to coordinate and can be used as a photoswitchable building block, with the photomagnetic characterisation evidencing a metastable state lifetime of the photo-induced valence tautomeric process of ca. 2.9 × 10(4) s below 20 K. The observed yields are higher than ones in similar systems, showing that tiny changes in the molecular structures may have a huge impact.

  15. Crystallographic and online spectral evidence for role of conformational change and conserved water in cytochrome oxidase proton pump.

    PubMed

    Liu, Jian; Qin, Ling; Ferguson-Miller, Shelagh

    2011-01-25

    Crystal structures in both oxidized and reduced forms are reported for two bacterial cytochrome c oxidase mutants that define the D and K proton paths, showing conformational change in response to reduction and the loss of strategic waters that can account for inhibition of proton transfer. In the oxidized state both mutants of the Rhodobacter sphaeroides enzyme, D132A and K362M, show overall structures similar to wild type, indicating no long-range effects of mutation. In the reduced state, the mutants show an altered conformation similar to that seen in reduced wild type, confirming this reproducible, reversible response to reduction. In the strongly inhibited D132A mutant, positions of residues and waters in the D pathway are unaffected except in the entry region close to the mutation, where a chloride ion replaces the missing carboxyl and a 2-Å shift in N207 results in loss of its associated water. In K362M, the methionine occupies the same position as the original lysine, but K362- and T359-associated waters in the wild-type structure are missing, likely accounting for the severe inhibition. Spectra of oxidized frozen crystals taken during X-ray radiation show metal center reduction, but indicate development of a strained configuration that only relaxes to a native form upon annealing. Resistance of the frozen crystal to structural change clarifies why the oxidized conformation is observable and supports the conclusion that the reduced conformation has functional significance. A mechanism is described that explains the conformational change and the incomplete response of the D-path mutant.

  16. Comparison of the duration and power spectral changes of monopolar and bipolar M waves caused by alterations in muscle fibre conduction velocity.

    PubMed

    Rodriguez-Falces, Javier; Navallas, Javier; Malanda, Armando; Rodriguez-Martin, Olivia

    2014-08-01

    The muscle compound action potential (M wave) recorded under monopolar configuration reflects both the propagation of the action potentials along the muscle fibres and their extinction at the tendon. M waves recorded under a bipolar configuration contain less cross talk and noise than monopolar M waves, but they do not contain the entire informative content of the propagating potential. The objective of this study was to compare the effect of changes in muscle fibre conduction velocity (MFCV) on monopolar and bipolar M waves and how this effect depends on the distance between the recording electrodes and tendon. The study was based on a simulation approach and on an experimental investigation of the characteristics of surface M waves evoked in the vastus lateralis during 4-s step-wise isometric contractions in knee extension at 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% MVC. The peak-to-peak duration (Durpp) and median frequency (Fmedian) of the M waves were calculated. For monopolar M waves, changes in Durpp and Fmedian produced by MFCV depended on the distance from the electrode to the tendon, whereas, for bipolar M waves, changes in Durpp and Fmedian were largely independent of the electrode-to-tendon distance. When the distance between the detection point and tendon lay between approximately 15 and 40mm, changes in Durpp of bipolar M waves were more pronounced than those of distal monopolar M waves but less marked than those of proximal monopolar M waves, and the opposite occurred for Fmedian. Since, for bipolar M waves, changes in duration and power spectral features produced by alterations in MFCV are not influenced by the electrode-to-tendon distance, the bipolar electrode configuration is a preferable choice over monopolar arrangements to estimate changes in conduction velocity.

  17. Spectral characterization of the binding and conformational changes of serum albumins upon interaction with an anticancer drug, anastrozole

    NASA Astrophysics Data System (ADS)

    Punith, Reeta; Seetharamappa, J.

    2012-06-01

    The present study employed different optical spectroscopic techniques viz., fluorescence, FTIR, circular dichroism (CD) and UV-vis absorption spectroscopy to investigate the mechanism of interaction of an anticancer drug, anastrozole (AZ) with transport proteins viz., bovine serum albumin (BSA) and human serum albumin (HSA). The drug, AZ quenched the intrinsic fluorescence of protein and the analysis of results revealed the presence of dynamic quenching mechanism. The binding characteristics of drug-protein were computed. The thermodynamic parameters, enthalpy change (ΔH°) and entropy change (ΔS°) were calculated to be +92.99 kJ/mol and +159.18 J/mol/K for AZ-BSA and, +99.43 kJ/mol and +159.19 J/mol/K for AZ-HSA, respectively. These results indicated that the hydrophobic forces stabilized the interaction between the drug and protein. CD, FTIR, absorption, synchronous and 3D fluorescence results indicated that the binding of AZ to protein induced structural perturbation in both serum albumins. The distance, r between the drug and protein was calculated based on the theory of Förster's resonance energy transfer and found to be 5.9 and 6.24 nm, respectively for AZ-BSA and AZ-HSA.

  18. In vivo spectral and fluorescence imaging microscopy of tumor microvessel blood supply and oxygenation changes following vascular targeting agent treatment

    NASA Astrophysics Data System (ADS)

    Lee, Jennifer; Kozikowski, Raymond; Molnar, Nikolett; Siemann, Dietmar W.; Sorg, Brian S.

    2012-03-01

    The formation of new microvasculature is essential for a tumor mass to grow. Vascular targeting agents (VTAs), including anti-angiogenic drugs and vascular disrupting agents, aim to either inhibit new vasculature growth or destroy existing vasculature, respectively. Because the mechanisms for anti-angiogenic drugs and vascular disrupting agents are complementary, analysis of these drugs used together is under investigation for the enhanced treatment of tumors in comparison to each treatment alone. The preclinical evaluation of the effects of VTAs on tumor growth in small animal models is vital for the development of effective drugs for clinical use. In vivo hyperspectral imaging microscopy of hemoglobin saturation has been used previously to investigate the efficacy of VTAs through analysis of tumor microvessel oxygenation after drug administration. Combining this imaging modality with first-pass fluorescence angiographic imaging can give additional important information about the vessel morphology and blood flow changes that occur after VTA treatment, thus elucidating the relationship between microvessel structure changes and oxygenation. In this study, we report the combined use of hyperspectral and first pass fluorescence angiographic imaging to examine the relationship between vessel morphology and oxygenation of human prostate cancer tumors in mice following treatment with vascular disrupting agents, OXi4503, and anti-VEGF angiogenesis inhibitor, cediranib. Imaging of the tumors is completed before treatment as well as in the days following treatment.

  19. [Urban vegetation coverage change inside the Third-Ring Road of Shenyang City, China: a study with linear spectral unmixing technique].

    PubMed

    Hu, Jian-Bo; Chen, Wei; Li, Xiao-Yu; He, Xing-Yuan

    2009-05-01

    Based on the Landsat TM images of 2001 and 2006, and by using linear spectral unmixing (LSU) technique, the information of urban vegetation coverage inside the Third-Ring Road of Shenyang City was extracted, and the dynamic change of the vegetation coverage in 2001-2006 was analyzed, in combining with a land use map derived from the visual interpretation of a QuickBird image of 2006. The results showed that in 2001-2006, the urban vegetation coverage in study area changed drastically. Urban greening and the cropland encroachment caused by urban sprawl coexisted, and the vegetation gain from urban greening was larger than the vegetation loss from cropland encroachment. The vegetation coverage of road, residence, public facilities, and park and square increased with varying degrees (5%-9%), while industrial land changed little. The spatial distribution of urban greening was relatively reasonable. Though the polarization of vegetation coverage between central city and suburban still existed, this polarization had been mitigated to some extent. With the increase of the distance from city center, the vegetation coverage increased in sequence of park and square (0.8% x km(-1)) < residence (1.5% x km(-1)) < industrial land (1.7% x km(-1)) < public facilities (2.4% x km(-1)) < road (2.9% x km(-1)). The polarization of vegetation coverage in public facilities and road were still serious, suggesting that more greening programs and strict conservation efforts were needed.

  20. Fullerene-Assisted Photoinduced Charge Transfer of Single-Walled Carbon Nanotubes through a Flavin Helix.

    PubMed

    Mollahosseini, Mehdi; Karunaratne, Erandika; Gibson, George N; Gascón, Jose A; Papadimitrakopoulos, Fotios

    2016-05-11

    One of the greatest challenges with single-walled carbon nanotube (SWNT) photovoltaics and nanostructured devices is maintaining the nanotubes in their pristine state (i.e., devoid of aggregation and inhomogeneous doping) so that their unique spectroscopic and transport characteristics are preserved. To this effect, we report on the synthesis and self-assembly of a C60-functionalized flavin (FC60), composed of PCBM and isoalloxazine moieties attached on either ends of a linear, C-12 aliphatic spacer. Small amounts of FC60 (up to 3 molar %) were shown to coassembly with an organic soluble derivative of flavin (FC12) around SWNTs and impart effective dispersion and individualization. A key annealing step was necessary to perfect the isoalloxazine helix and expel the C60 moiety away from the nanotubes. Steady-state and transient absorption spectroscopy illustrate that 1% or higher incorporation of FC60 allows for an effective photoinduced charge transfer quenching of the encased SWNTs through the seamless helical encase. This is enabled via the direct π-π overlap between the graphene sidewalls, isoalloxazine helix, and the C60 cage that facilitates SWNT exciton dissociation and electron transfer to the PCBM moiety. Atomistic molecular simulations indicate that the stability of the complex originates from enhanced van der Waals interactions of the flexible spacer wrapped around the fullerene that brings the C60 in π-π overlap with the isoalloxazine helix. The remarkable spectral purity (in terms of narrow E(S)ii line widths) for the resulting ground-state complex signals a new class of highly organized supramolecular nanotube architecture with profound importance for advanced nanostructured devices.

  1. Self-assembly of semiconductor organogelator nanowires for photoinduced charge separation.

    PubMed

    Wicklein, André; Ghosh, Suhrit; Sommer, Michael; Würthner, Frank; Thelakkat, Mukundan

    2009-05-26

    We investigated an innovative concept of general validity based on an organogel/polymer system to generate donor-acceptor nanostructures suitable for charge generation and charge transport. An electron conducting (acceptor) perylene bisimide organogelator forms nanowires in suitable solvents during gelation process. This phenomenon was utilized for its self-assembly in an amorphous hole conducting (donor) polymer matrix to realize an interpenetrating donor-acceptor interface with inherent morphological stability. The self-assembly and interface generation were carried out either stepwise or in a single-step. Morphology of the donor-acceptor network in thin films obtained via both routes were studied by a combination of scanning electron microscopy and atomic force microscopy. Additionally, photoinduced charge separation and charge transport in these systems were tested in organic solar cells. Fabrication steps of multilayer organogel/polymer photovoltaic devices were optimized with respect to morphology and surface roughness by introducing additional smoothening layers and charge injection/blocking layers. An inverted cell geometry was used here in which electrons are collected at the bottom electrode and holes at the top electrode. The simultaneous preparation of the interface exhibits almost 3-fold improvement in device characteristics compared to the successive method. The device characteristics under AM1.5 spectral conditions and 100 mW/cm(2) for the simultaneous preparation route are short circuit current J(sc) = 0.28 mA cm(-2), open circuit voltage V(OC) = 390 mV, fill factor FF = 38%, and a power conversion efficiency eta = 0.041%.

  2. Direct characterization of photoinduced lattice dynamics in BaFe2As2.

    PubMed

    Gerber, S; Kim, K W; Zhang, Y; Zhu, D; Plonka, N; Yi, M; Dakovski, G L; Leuenberger, D; Kirchmann, P S; Moore, R G; Chollet, M; Glownia, J M; Feng, Y; Lee, J-S; Mehta, A; Kemper, A F; Wolf, T; Chuang, Y-D; Hussain, Z; Kao, C-C; Moritz, B; Shen, Z-X; Devereaux, T P; Lee, W-S

    2015-06-08

    Ultrafast light pulses can modify electronic properties of quantum materials by perturbing the underlying, intertwined degrees of freedom. In particular, iron-based superconductors exhibit a strong coupling among electronic nematic fluctuations, spins and the lattice, serving as a playground for ultrafast manipulation. Here we use time-resolved X-ray scattering to measure the lattice dynamics of photoexcited BaFe2As2. On optical excitation, no signature of an ultrafast change of the crystal symmetry is observed, but the lattice oscillates rapidly in time due to the coherent excitation of an A1g mode that modulates the Fe-As-Fe bond angle. We directly quantify the coherent lattice dynamics and show that even a small photoinduced lattice distortion can induce notable changes in the electronic and magnetic properties. Our analysis implies that transient structural modification can be an effective tool for manipulating the electronic properties of multi-orbital systems, where electronic instabilities are sensitive to the orbital character of bands.

  3. Spectral Mixture Analysis (SMA) of Landsat Imagery for Land Cover Change Study of Highly Degraded Peatland in Indonesia

    NASA Astrophysics Data System (ADS)

    Sakti, A. D.; Tsuyuki, S.

    2015-04-01

    Indonesian peatland, one of the world's largest tropical peatlands, is facing immense anthropogenic pressures such as illegal logging, degradation and also peat fires, especially in fertile peatlands. However, there still is a lack of appropriate tools to assess peatland land cover change. By taking Pelalawan district located in Sumatra Island, this study determines number of land cover endmembers that can be detected and mapped using new generation of Landsat 8 OLI in order to develop highquality burned peat fraction images. Two different image transformations, i.e. Principle Component Analysis (PCA), Minimum Noise Fraction (MNF) and two different scatterplot analyses, i.e. global and local, were tested and their accuracy results were compared. Analysis of image dimensionality was reduced by using PCA. Pixel Purity Index (PPI), formed by using MNF, was used to identify pure pixel. Four endmembers consisting of two types of soil (peat soil and dry soil) and two types of vegetation (peat vegetation and dry vegetation) were identified according to the scatterplot and their associated interpretations were obtained from the Pelalawan Fraction model. The results showed that local scatterplot analysis without PPI masking can detect high accuracy burned peat endmember and reduces RMSE value of fraction image to improve classification accuracy.

  4. Spectral Predictors

    SciTech Connect

    Ibarria, L; Lindstrom, P; Rossignac, J

    2006-11-17

    Many scientific, imaging, and geospatial applications produce large high-precision scalar fields sampled on a regular grid. Lossless compression of such data is commonly done using predictive coding, in which weighted combinations of previously coded samples known to both encoder and decoder are used to predict subsequent nearby samples. In hierarchical, incremental, or selective transmission, the spatial pattern of the known neighbors is often irregular and varies from one sample to the next, which precludes prediction based on a single stencil and fixed set of weights. To handle such situations and make the best use of available neighboring samples, we propose a local spectral predictor that offers optimal prediction by tailoring the weights to each configuration of known nearby samples. These weights may be precomputed and stored in a small lookup table. We show that predictive coding using our spectral predictor improves compression for various sources of high-precision data.

  5. Spectral power and functional connectivity changes during mindfulness meditation with eyes open: A magnetoencephalography (MEG) study in long-term meditators.

    PubMed

    Wong, W P; Camfield, D A; Woods, W; Sarris, J; Pipingas, A

    2015-10-01

    Whilst a number of previous studies have been conducted in order to investigate functional brain changes associated with eyes-closed meditation techniques, there is a relative scarcity in the literature with regards to changes occurring during eyes-open meditation. The current project used magnetoencephalography (MEG) to investigate differences in spectral power and functional connectivity between 11 long-term mindfulness meditators (LTMMs) with >5 years of experience and 12 meditation-naïve control participants both during baseline eyes-open rest and eyes-open open-monitoring (OM) mindfulness meditation. During resting with eyes-open, prior to meditating, greater mean alpha power was observed for LTMMs in comparison to controls. However, during the course of OM meditation, a significantly greater increase in theta power was observed over a broad fronto-centro-parietal region for control participants in comparison to LTMMs. In contrast, whole-head mean connectivity was found to be significantly greater for long-term meditators in comparison to controls in the theta band both during rest as well as during meditation. Additionally, mean connectivity was significantly lower for long-term meditators in the low gamma band during rest and significantly lower in both low and high gamma bands during meditation; and the variance of low-gamma connectivity scores for long-term meditators was significantly decreased compared to the control group. The current study provides important new information as to the trait functional changes in brain activity associated with long-term mindfulness meditation, as well as the state changes specifically associated with eyes-open open monitoring meditation techniques.

  6. Fourth-order perturbative model for photoinduced internal conversion processes.

    PubMed

    Molesky, Brian P; Moran, Andrew M

    2013-12-27

    Essential to the functionality of numerous biological and synthetic molecular systems is the ability to rapidly convert electronic excitation energy into heat. Such internal conversion (IC) transitions often cannot be described by traditional second-order kinetic theories because of time-coincident electronic and nuclear relaxation processes. Here, we present a perturbative fourth-order phenomenological model for photoinduced IC that incorporates effects associated with finite laser bandwidths and nonequilibrium nuclear motions. Specialized knowledge of first-principles computational methods is not required, and many parameters can be obtained with standard spectroscopic measurements. The model is applied to the IC processes that precede electrocyclic ring-opening in α-terpinene. It is shown that the primary factor governing the shape of the population decay profile (Gaussian versus exponential) is the rate at which the wavepacket approaches the geometry corresponding to degeneracy between the excited states. Other parameters such as the displacement in the promoting mode and the thermal fluctuation amplitudes affect the sensitivity of the IC dynamics to motion of the wavepacket but do not alter the basic physical picture. Finally, we suggest a wavepacket representation of the IC process to visualize correlations between population-transfer dynamics and the amount of energy transferred from the system to the bath.

  7. Photoinduced Bimolecular Electron Transfer from Cyano Anions in Ionic Liquids.

    PubMed

    Wu, Boning; Liang, Min; Maroncelli, Mark; Castner, Edward W

    2015-11-19

    Ionic liquids with electron-donating anions are used to investigate rates and mechanisms of photoinduced bimolecular electron transfer to the photoexcited acceptor 9,10-dicyanoanthracene (9,10-DCNA). The set of five cyano anion ILs studied comprises the 1-ethyl-3-methylimidazolium cation paired with each of these five anions: selenocyanate, thiocyanate, dicyanamide, tricyanomethanide, and tetracyanoborate. Measurements with these anions dilute in acetonitrile and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide show that the selenocyanate and tricyanomethanide anions are strong quenchers of the 9,10-DCNA fluorescence, thiocyanate is a moderately strong quencher, dicyanamide is a weak quencher, and no quenching is observed for tetracyanoborate. Quenching rates are obtained from both time-resolved fluorescence transients and time-integrated spectra. Application of a Smoluchowski diffusion-and-reaction model showed that the complex kinetics observed can be fit using only two adjustable parameters, D and V0, where D is the relative diffusion coefficient between donor and acceptor and V0 is the value of the electronic coupling at donor-acceptor contact.

  8. Electric Field Dependence of Photo-Induced Field Emission Current.

    NASA Astrophysics Data System (ADS)

    Egert, Charles Michael

    We have measured the photo-induced field emission current from a tungsten field emitter as a function of electric field. These experiments were performed with a retardation energy analyzer to measure total current and a 127(DEGREES) cylindrical differential energy analyzer to measure the energy resolved PFE current. The results of these experiments are compared with a simple theory of PFE, developed by Schwartz and Schaich, which is an extension of field emission theory including the surface photoeffect, but assuming constant photoexcitation matrix elements. Our experimental results disagree with this theory in two ways: First, for high fields and photon energy (electrons emitted above the field emission barrier maximum) theory predicts a larger increase in PFE current than is observed experimentally. Second, we have also confirmed the existence of a field dependent oscillatory component of the PFE current emitted from the W(110) surface with photon energies of 2.7 eV and 3.5 eV. The simple theory described here, as well as more sophisticated calculations, have been unable to explain this oscillatory feature. We have also reported, for the first time, the field dependence of the energy resolved PFE current measured with a 127(DEGREES) cylindrical energy analyzer. These preliminary results show evidence of the oscillatory component previously only observed in the total PFE current.

  9. Highly Twisted Triarylamines for Photoinduced Intramoleculer ChargeTransfer

    SciTech Connect

    Chudomel, J. M.; Yang, B. Q.; Barnes, M. D.; Achermann, M.; Mague, J. T.; Lahti, P. M.

    2011-08-04

    9-(N,N-Dianisylamino)anthracene (9DAAA), 9-(N,N-dianisylamino)dinaphth([1,2-a:2'-1'-j]-anthracene (9DAAH), and 9,10-bis(N,N-dianisylamino)anthracene (910BAA) were synthesized as highly twisted triarylamines with potential for photoexcited internal charge transfer. Crystallography of 9DAAA shows its dianisylamino group to be twisted nearly perpendicular to its anthracene unit, similar to a report for 910BAA. The solution fluorescence spectra show strong bathochromic shifts for each of the three molecular systems with strongly decreased quantum efficiency in higher polarity solvents. Solution-phase (ensemble) time-resolved photoluminescence measurements show up to 4-fold decreases in fluorescence lifetime in acetonitrile compared to hexane. The combined results are consistent with photoinduced, transient intramolecular charge-transfer from the bis-anisylamine unit to the polycyclic aromatic unit. Computational modeling is in accord with intramolecular transfer of electron density from the bis-anisylamino unit to the anthracene, based on in comparisons of HOMO and LUMO.

  10. Mode of photo-induced toxic action of PAH in fish

    SciTech Connect

    Weinstein, J.E.; Oris, J.T.; Taylor, D.H.

    1995-12-31

    Juvenile fathead minnows (Pimephales promelas) were exposed to 0, 6, and 12 {micro}g/L fluoranthene in the presence of ultraviolet (US) light for 6, 12, 24, 48 and 96 hours. Ultrastructural pathology of the secondary gill lamellae was examined using transmission electron microscopy. Following 12 hours of exposure to 12 {micro}g/L fluoranthene and UV light, epithelial cells appeared highly vacuolated and swollen. Following 48 hours, additional morphological alterations in epithelial cells included multivesiculated blebbing of the plasma membrane into intercellular gaps, numerous cytolysosomes, myelinoid bodies, and enlarged lysosomes with lipid-like contents. The staining characteristics of these cytoplasmic inclusions were consistent with that of phospholipid autodigestion. In addition, an inflammatory-type reaction occurred in the secondary lamellae following 24 hours of exposure. This reaction was characterized by large areas of intercellular edema, which produced a lifting of the epithelium, and the occasional presence of macrophages and granulocytes within the edematous areas and the lamellar blood sinuses. No morphological changes were observed in chloride cells, mucous cells, or pillar cells. In those fish exposed to 6 {micro}g/L fluoranthene and UV light, a similar progression compared to 12 {micro}g/L exposure of epithelial cell damage and inflammatory-type reaction was evident beginning at 24 hours of exposure. The results of this study suggest that the mode of action of photo-induced fluoranthene toxicity in fish is respiratory stress.

  11. Steady-state and femtosecond photoinduced processes of blepharismins bound to alpha-crystallin.

    PubMed

    Youssef, T; Brazard, J; Ley, C; Lacombat, F; Plaza, P; Martin, M M; Sgarbossa, A; Checcucci, G; Lenci, F

    2008-07-01

    The interaction of blepharismin (BP) and oxyblepharismin (OxyBP) with bovine alpha-crystallin (BAC) has been studied both by steady-state and femtosecond spectroscopy, with the aim of assessing the possible phototoxicity of these compounds toward the eye tissues. We showed that these pigments form with BAC potentially harmful ground-state complexes, the dissociation constants of which have been estimated to be 6 +/- 2 micromol L(-1) for OxyBP and 9 +/- 4 micromol L(-1) for BP. Irradiation with steady-state visible light of solutions of blepharismins in the presence of BAC proved to induce a quenching of both the pigment and the intrinsic protein fluorescences. These effects were tentatively rationalized in terms of structural changes of alpha-crystallin. On the other hand, femtosecond transient absorption spectroscopy was used to check the occurrence of any type I photoactivity of oxyblepharismin bound to alpha-crystallin. The existence of a particular type of fast photoinduced reaction, not observed in former studies with human serum albumin but present in the natural oxyblepharismin-binding protein, could here be evidenced but no specific reaction was observed during the first few nanoseconds after excitation. Partial denaturation of alpha-crystallin was however found to alter the excited-state behaviour of its complex with oxyblepharismin, making it partly resemble that of free oxyblepharismin in solution.

  12. Photoinduced electron transfer in a protein-surfactant complex: probing the interaction of SDS with BSA.

    PubMed

    Chakraborty, Anjan; Seth, Debabrata; Setua, Palash; Sarkar, Nilmoni

    2006-08-24

    Photoinduced fluorescence quenching electron transfer from N,N-dimethyl aniline to different 7-amino coumarin dyes has been investigated in sodium dodecyl sulfate (SDS) micelles and in bovine serum albumin (BSA)-SDS protein-surfactant complexes using steady state and picosecond time resolved fluorescence spectroscopy. The electron transfer rate has been found to be slower in BSA-SDS protein-surfactant complexes compared to that in SDS micelles. This observation has been explained with the help of the "necklace-and-bead" structure formed by the protein-surfactant complex due to coiling of protein molecules around the micelles. In the correlation of free energy change to the fluorescence quenching electron transfer rate, we have observed that coumarin 151 deviates from the normal Marcus region, showing retardation in the electron transfer rate at higher negative free energy region. We endeavored to establish that the retardation in the fluorescence quenching electron transfer rate for coumarin 151 at higher free energy region is a result of slower rotational relaxation and slower translational diffusion of coumarin 151 (C-151) compared to its analogues coumarin 152 and coumarin 481 in micelles and in protein-surfactant complexes. The slower rotational relaxation and translational diffusion of C-151 are supposed to be arising from the different location of coumarin 151 compared to coumarin 152 and coumarin 481.

  13. Side chain variations on a series of dicyanovinyl-terthiophenes: a photoinduced absorption study.

    PubMed

    Ziehlke, Hannah; Fitzner, Roland; Koerner, Christian; Gresser, Roland; Reinold, Egon; Bäuerle, Peter; Leo, Karl; Riede, Moritz K

    2011-08-04

    We characterize a series of dicyanovinyl-terthiophenes with different alkyl side chains. Variations of side chain substitution patterns and length mainly affect the morphology of the evaporated thin films, which in turn sensitively influences properties like absorption, energy levels, and thin film roughness. To investigate changes in transfer processes between electron donor (D) and acceptor (A) molecules due to side chain variations, we use photoinduced absorption spectroscopy (PIA). PIA probes the long-living photoexcited species at the D-A interface: triplet excitons, cations, and anions. For a blend layer of dicyanovinyl-terthiophene and the electron acceptor fullerene C(60), an energy transfer via the singlet and triplet manifold of C(60) occurs. The recombination dynamics of the triplet excitons reveal two components that differ in their lifetime and generation rate by 1 order of magnitude. By comparing the dynamics of triplet excitons in neat and blend layers, we estimate the energy transfer efficiency in dependence of the type of side chain. The compound with methyl side chains shows remarkable properties regarding thin film absorption, surface roughness, and energy transfer efficiency, which we attribute to the specific nanomorphology of the thin film.

  14. Retardation of the orientation relaxation of azo-dye doped amorphous polymers upon photoinduced isomerization

    NASA Astrophysics Data System (ADS)

    Chan, S. W.; Quatela, A.; Casalboni, M.; Nunzi, J.-M.

    2006-08-01

    The orientation relaxation upon photo-induced isomerization of azo-dyes was studied. All-optical poling (AOP) and photo-induced birefringence, which are based on the mechanism of angular selective photo-isomerization, were employed to manipulate the angular distribution of azo-dyes (Disperse-red 1) doped in three different amorphous polymers: (poly(methyl methacrylate) PMMA, poly(carbonate) PC and poly(sulfone) PSU), with different glass transition temperature (T g). In the case of AOP, quasi-permanent macroscopic second-order nonlinear optical susceptibility χ (2) was inscribed in the dye-doped centro-symmetric polymer systems, while in the case of photo-induced birefringence, quasi-permanent birefringence Δn was inscribed in the dye-doped isotropic polymer systems. Relaxation of χ (2) and Δn were monitored upon different duration of AOP and photo-induced birefringence preparation. Experimental results show that azo-dye orientation relaxation follows the duration of the photo-nduced isomerization process: the longer the photo-induced isomerization process, the slower the relaxation of the inscribed χ (2) and Δn. In addition, retardation of the orientation relaxation does not follow a simple relation with hardness (T g) of the polymer host. Causes of the orientation relaxation retardation are discussed.

  15. QSARs for photo-induced toxicity of polycyclic aromatic hydrocarbons (PAHs)

    SciTech Connect

    Mekenyan, O.; Call, D.; Ankley, G.; Veith, G.

    1994-12-31

    Photo-induced toxicity of polycyclic aromatic hydrocarbons (PAHs) was found to be a result of competing internal and external factors which interact to produce a complex, multilinear relationship between toxicity and chemical structure. The relationship between molecular electronic structure and photo-dynamic effects was studied in both ground and excited states. A measure of the energy required for an electron to be elevated from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), or HOMO-LUMO gap, provided a useful ground state index to explain the persistence, light absorption, and eventual photo-induced toxicity of PAHs to Daphnia magna. The derived QSARs clearly distinguished photo-induced toxicity differences between pairs of structurally similar PAHs, such as phenanthrene and anthracene, benzo[a]anthracene and tetracene, etc. Those PAHs exhibiting photo-induced toxicity were consistently within a specific HOMO-LUMO gap range. The relationship between the excited state electronic parameters and toxicity was also studied. Significant correlations were found with the measured energies of singlet and triplet states from spectroscopic data. An investigation of the effect of substituent additions on photo-induced acute toxicity of parent PAHs revealed that alkyl and hydroxy moieties did not significantly reduce the HOMO-LUMO gap of the parent PAHs. Nitro, alkene and chloro substituents cause gap reductions, whereby certain derivatives of parent chemicals that were close to the ``toxic region`` of the electronic gap could become phototoxic with such additions.

  16. Infrared imaging as a cancer diagnostic tool: introducing a new concept of spectral barcodes for identifying molecular changes in colon tumors.

    PubMed

    Nallala, Jayakrupakar; Piot, Olivier; Diebold, Marie-Danièle; Gobinet, Cyril; Bouché, Olivier; Manfait, Michel; Sockalingum, Ganesh D

    2013-03-01

    Complementary diagnostic methods to conventional histopathology are under scrutiny for various types of cancers for rapid and molecular level diagnostics. In this perspective, a biophotonic approach based on infrared spectral micro-imaging combined with multivariate statistical analysis has been implemented on colon tissues. The ability of infrared imaging to investigate the intrinsic biochemical features of cells and tissues has been exploited to develop a new concept of spectral bar coding. To implement this concept, 10 frozen colon tissue samples (five nontumoral and tumoral pairs from five patients) were imaged using infrared spectral micro-imaging in a nondestructive manner. The spectral images were processed by a multivariate clustering method to identify the histological organization in a label-free manner. Spectral information from the epithelial components was then automatically recovered on the basis of their intrinsic biochemical composition, and compared using a statistical method (Mann-Whitney U-test) to construct spectral barcodes specific to each patient. The spectral barcodes representing the discriminant infrared spectral wavenumbers (900-1,800 cm(-1) ) enabled characterization of some of the malignancy-associated biochemical alterations associated with mucin, nucleotides, carbohydrates, and protein regions. This approach not only allowed the identification of common biochemical alterations among all the colon cancer patients, but also revealed a difference of gradient within individual patients. This new concept of spectral bar coding gives insight into the potential of infrared spectral micro-imaging as a complementary diagnostic tool to conventional histopathology, for biochemical level understanding of malignancy in colon cancers in an objective and label-free manner.

  17. Determination of the spectral dependence of reduced scattering and quantitative second-harmonic generation imaging for detection of fibrillary changes in ovarian cancer

    NASA Astrophysics Data System (ADS)

    Campbell, Kirby R.; Tilbury, Karissa B.; Campagnola, Paul J.

    2015-03-01

    Here, we examine ovarian cancer extracellular matrix (ECM) modification by measuring the wavelength dependence of optical scattering measurements and quantitative second-harmonic generation (SHG) imaging metrics in the range of 800-1100 nm in order to determine fibrillary changes in ex vivo normal ovary, type I, and type II ovarian cancer. Mass fractals of the collagen fiber structure is analyzed based on a power law correlation function using spectral dependence measurements of the reduced scattering coefficient μs' where the mass fractal dimension is related to the power. Values of μs' are measured using independent methods of determining the values of μs and g by on-axis attenuation measurements using the Beer-Lambert Law and by fitting the angular distribution of scattering to the Henyey-Greenstein phase function, respectively. Quantitativespectral SHG imaging on the same tissues determines FSHG/BSHG creation ratios related to size and harmonophore distributions. Both techniques probe fibril packing order, but the optical scattering probes structures of sizes from about 50-2000 nm where SHG imaging - although only able to resolve individual fibers - builds contrast from the assembly of fibrils. Our findings suggest that type I ovarian tumor structure has the most ordered collagen fibers followed by normal ovary then type II tumors showing the least order.

  18. Self-organization and photo-induced formation of cyanine dye aggregates on the plasmonic Ag nanoparticles

    NASA Astrophysics Data System (ADS)

    Starovoytov, Anton A.; Nabiullina, Rezida D.; Toropov, Nikita A.

    2016-04-01

    The optical properties of hybrid film based on plasmon Ag nanoparticles of different size and cyanine dyes with different length of conjugation chain depending on the relative position of the plasmon resonance and the absorption of organic molecules were studied. The absorption spectra of the films revealed several molecular forms, such as all-trans- and cisisomers, dimers and J-aggregate, which also exist in pure organic films without Ag nanoparticles. It's shown that the absorption of aggregate bands increased after exposure by nanosecond laser on the hybrid films due to photo-induced additional self-organization of aggregates. In the presence of Ag nanoparticles, laser radiation leads to the change of molecular forms at a comparatively low threshold.

  19. Light-Activated Protein Inhibition through Photoinduced Electron Transfer of a Ruthenium(II)–Cobalt(III) Bimetallic Complex

    PubMed Central

    Holbrook, Robert J.; Weinberg, David J.; Peterson, Mark D.; Weiss, Emily A.; Meade, Thomas J.

    2015-01-01

    We describe a mechanism of light activation that initiates protein inhibitory action of a biologically inert Co(III) Schiff base (Co(III)-sb) complex. Photoinduced electron transfer (PET) occurs from a Ru(II) bipyridal complex to a covalently attached Co(III) complex and is gated by conformational changes that occur in tens of nanoseconds. Reduction of the Co(III)-sb by PET initiates displacement of the inert axial imidazole ligands, promoting coordination to active site histidines of α-thrombin. Upon exposure to 455 nm light, the rate of ligand exchange with 4-methylimidazole, a histidine mimic, increases by approximately 5-fold, as observed by NMR spectroscopy. Similarly, the rate of α-thrombin inhibition increases over 5-fold upon irradiation. These results convey a strategy for light activation of inorganic therapeutic agents through PET utilizing redox-active metal centers. PMID:25671465

  20. Light-activated protein inhibition through photoinduced electron transfer of a ruthenium(II)–cobalt(III) bimetallic complex

    DOE PAGES

    Holbrook, Robert J.; Weinberg, David J.; Peterson, Mark D.; ...

    2015-02-11

    In this paper, we describe a mechanism of light activation that initiates protein inhibitory action of a biologically inert Co(III) Schiff base (Co(III)-sb) complex. Photoinduced electron transfer (PET) occurs from a Ru(II) bipyridal complex to a covalently attached Co(III) complex and is gated by conformational changes that occur in tens of nanoseconds. Reduction of the Co(III)-sb by PET initiates displacement of the inert axial imidazole ligands, promoting coordination to active site histidines of α-thrombin. Upon exposure to 455 nm light, the rate of ligand exchange with 4-methylimidazole, a histidine mimic, increases by approximately 5-fold, as observed by NMR spectroscopy. Similarly,more » the rate of α-thrombin inhibition increases over 5-fold upon irradiation. Finally, these results convey a strategy for light activation of inorganic therapeutic agents through PET utilizing redox-active metal centers.« less

  1. Light-activated protein inhibition through photoinduced electron transfer of a ruthenium(II)–cobalt(III) bimetallic complex

    SciTech Connect

    Holbrook, Robert J.; Weinberg, David J.; Peterson, Mark D.; Weiss, Emily A.; Meade, Thomas J.

    2015-02-11

    In this paper, we describe a mechanism of light activation that initiates protein inhibitory action of a biologically inert Co(III) Schiff base (Co(III)-sb) complex. Photoinduced electron transfer (PET) occurs from a Ru(II) bipyridal complex to a covalently attached Co(III) complex and is gated by conformational changes that occur in tens of nanoseconds. Reduction of the Co(III)-sb by PET initiates displacement of the inert axial imidazole ligands, promoting coordination to active site histidines of α-thrombin. Upon exposure to 455 nm light, the rate of ligand exchange with 4-methylimidazole, a histidine mimic, increases by approximately 5-fold, as observed by NMR spectroscopy. Similarly, the rate of α-thrombin inhibition increases over 5-fold upon irradiation. Finally, these results convey a strategy for light activation of inorganic therapeutic agents through PET utilizing redox-active metal centers.

  2. Spectral-finite element approach to post-seismic relaxation in a spherical compressible Earth: application to gravity changes due to the 2004 Sumatra-Andaman earthquake

    NASA Astrophysics Data System (ADS)

    Tanaka, Y.; Hasegawa, T.; Tsuruoka, H.; Klemann, V.; Martinec, Z.

    2015-01-01

    Global navigation satellite systems (GNSSs) have revealed that a mega-thrust earthquake that occurs in an island-arc trench system causes post-seismic crustal deformation. Such crustal deformation data have been interpreted by combining three mechanisms: afterslip, poroelastic rebound and viscoelastic relaxation. It is seismologically important to determine the contribution of each mechanism because it provides frictional properties between the plate boundaries and viscosity estimates in the asthenosphere which are necessary to evaluate the stress behaviour during earthquake cycles. However, the observation sites of GNSS are mostly deployed over land and can detect only a small part of the large-scale deformation, which precludes a clear separation of the mechanisms. To extend the spatial coverage of the deformation area, recent studies started to use satellite gravity data that can detect long-wavelength deformations over the ocean. To date, compared with theoretical models for calculating the post-seismic crustal deformation, a few models have been proposed to interpret the corresponding gravity variations. Previous approaches have adopted approximations for the effects of compressibility, sphericity and self-gravitation when computing gravity changes. In this study, a new spectral-finite element approach is presented to consider the effects of material compressibility for Burgers viscoelastic earth model with a laterally heterogeneous viscosity distribution. After the basic principles are explained, it is applied to the 2004 Sumatra-Andaman earthquake. For this event, post-seismic deformation mechanisms are still a controversial topic. Using the developed approach, it is shown that the spatial patterns of gravity change generated by the above three mechanisms clearly differ from one another. A comparison of the theoretical simulation results with the satellite gravity data obtained from the Gravity Recovery and Climate Experiment reveals that both afterslip and

  3. Existence of a photoinducible phase for ovarian development and photoperiod-related alteration of clock gene expression in a damselfish.

    PubMed

    Takeuchi, Yuki; Hada, Noriko; Imamura, Satoshi; Hur, Sung-Pyo; Bouchekioua, Selma; Takemura, Akihiro

    2015-10-01

    The sapphire devil, Chrysiptera cyanea, is a reef-associated damselfish and their ovarian development can be induced by a long photoperiod. In this study, we demonstrated the existence of a photoinducible phase for the photoperiodic ovarian development in the sapphire devil. Induction of ovarian development under night-interruption light schedules and Nanda-Hamner cycles revealed that the photoinducible phase appeared in a circadian manner between ZT12 and ZT13. To characterize the effect of photoperiod on clock gene expression in the brain of this species, we determined the expression levels of the sdPer1, sdPer2, sdCry1, and sdCry2 clock genes under constant light and dark conditions (LL and DD) and photoperiodic (short and long photoperiods). The expression of sdPer1 exhibited clear circadian oscillation under both LL and DD conditions, while sdPer2 and sdCry1 expression levels were lower under DD than under LL conditions and sdCry2 expression was lower under LL than under DD conditions. These results suggest a key role for sdPer1 in circadian clock cycling and that sdPer2, sdCry1, and sdCry2 are light-responsive clock genes in the sapphire devil. After 1 week under a long photoperiod, we observed photoperiod-related changes in sdPer1, sdPer2, and sdCry2 expression, but not in sdCry1 expression. These results suggest that the expression patterns of some clock genes exhibit seasonal variation according to seasonal changes in day length and that such seasonal alteration of clock gene expression may contribute to seasonal recognition by the sapphire devil.

  4. Photo-induced Doping in GaN Epilayers with Graphene Quantum Dots

    PubMed Central

    Lin, T. N.; Inciong, M. R.; Santiago, S. R. M. S.; Yeh, T. W.; Yang, W. Y.; Yuan, C. T.; Shen, J. L.; Kuo, H. C.; Chiu, C. H.

    2016-01-01

    We demonstrate a new doping scheme where photo-induced carriers from graphene quantum dots (GQDs) can be injected into GaN and greatly enhance photoluminescence (PL) in GaN epilayers. An 8.3-fold enhancement of PL in GaN is observed after the doping. On the basis of time-resolved PL studies, the PL enhancement is attributed to the carrier transfer from GQDs to GaN. Such a carrier transfer process is caused by the work function difference between GQDs and GaN, which is verified by Kelvin probe measurements. We have also observed that photocurrent in GaN can be enhanced by 23-fold due to photo-induced doping with GQDs. The improved optical and transport properties from photo-induced doping are promising for applications in GaN-based optoelectronic devices. PMID:26987403

  5. Photoinduced Charge Transport in a BHJ Solar Cell Controlled by an External Electric Field

    PubMed Central

    Li, Yongqing; Feng, Yanting; Sun, Mengtao

    2015-01-01

    This study investigated theoretical photoinduced charge transport in a bulk heterojunction (BHJ) solar cell controlled by an external electric field. Our method for visualizing charge difference density identified the excited state properties of photoinduced charge transfer, and the charge transfer excited states were distinguished from local excited states during electronic transitions. Furthermore, the calculated rates for the charge transfer revealed that the charge transfer was strongly influenced by the external electric field. The external electric field accelerated the rate of charge transfer by up to one order when charge recombination was significantly restrained. Our research demonstrated that photoinduced charge transport controlled by an external electric field in a BHJ solar cell is efficient, and the exciton dissociation is not the limiting factor in organic solar cells.Our research should aid in the rational design of a novel conjugated system of organic solar cells. PMID:26353997

  6. Recent advances in photoinduced donor/acceptor copolymerization

    NASA Astrophysics Data System (ADS)

    Jönsson, S.; Viswanathan, K.; Hoyle, C. E.; Clark, S. C.; Miller, C.; Morel, F.; Decker, C.

    1999-05-01

    Photoinitiated free radical polymerization of donor (D)/acceptor (A) type monomers has gained considerable interest due to the possibility to efficiently photopolymerize non-acrylate based systems. Furthermore, this photoinduced alternating copolymerization can be accomplished without the presence of a conventional free radical generating photoinitiator. In the past, we have shown that the structural influences in the direct photolysis of N-Alkyl and N-Arylmaleimides as well as their corresponding ground state charge transfer complexes (CTC) with suitable donors have carefully been investigated. For certain combinations of A and D type monomers, a direct photolysis of the ground state complex or the excitation of the acceptor, followed by the formation of an exciplex, has been shown to initiate the copolymerization. Herein, we show that the main route of initiation is based on inter or intra molecular H-abstraction from an excited state maleimide, whereby no exciplex formation takes place. H-abstraction will predominantly take place in systems where easily abstractable hydrogens are present. Our laser flash photolysis investigation, ESR [1] (A. Hiroshi, I. Takasi, T. Nosi, Macromol. Chem. 190 (1989) 2821) and phosphorescence emissions [2,3] (K.S. Chen, T. Foster, J.K.S. Wan, J. Phys. Chem. 84 (1980) 2473; C.J. Seliskar, S.P. McGlynn, J. Chem. Phys. 55 (1971) 4337) studies show that triplet excited states of N-alkyl substituted maleimides (RMI), which are well known strong precursors for direct H-abstractions from aliphatic ethers and secondary alcohols, are formed upon excitation. Rates of copolymerization and degrees of conversion for copolymerization of maleimide/vinyl ether pairs in air and nitrogen have been measured as a function of hydrogen abstractability of the excited triplet state MI as well as the influence of concentration and hydrogen donating effect of the hydrogen donor.

  7. Photoinduced color centers creation in superionic crystals RbAg 4 I 5

    NASA Astrophysics Data System (ADS)

    Kovaleva, N.; Boris, A.; Bredikhin, S.; Awano, T.

    1995-12-01

    A new phenomenon of a reversible photoinduced coloration caused by light irradiation is discovered and investigated in superionic RbAg 4 I 5 crystals. The reversible photoinduced absorption is found to be a result of irradiation by light with wavelengths in the region from 420 nm to 450 nm. The proposed mechanism of the discovered effect is associated with ambipolar diffusion of screened by mobile ions optically excited electronic carriers. The processes of color centers creation in superionic crystals RbAg 4 I 5 due to additive coloring in iodine vapours, ionic implantation and ?-ray irradiation are considered.

  8. Determination of photoinduced and intrinsic birefringences in PMMA/DR13 guest-host film

    NASA Astrophysics Data System (ADS)

    Dall'Agnol, Fernando Fuzinatto; Shimizu, Flávio Makoto; Giacometti, José A.

    2014-07-01

    We report measurements and analysis of photoinduced birefringence (PIB) in polymeric stretched films, hence, with an intrinsic birefringence (IB) associated to the polymeric chain orientation. It was found that transmittance signal is dependent on the angle between the film stretching direction and the probe light polarization, increasing or decreasing relatively to IB signal. Theoretical analysis considered that light propagates through the film having a photoinduced and intrinsic birefringences with independent optical axes. The transmittance signal dependence on the film angle is correctly accounted and our approach could give a phenomenological elucidation to the effect known as the inverse relaxation effect.

  9. Stretched exponential kinetics for photoinduced birefringence in azo dye doped PVA films

    NASA Astrophysics Data System (ADS)

    Yang, Hye Ri; Kim, Eun Ju; Lee, Sang Jo; Kim, Gun Yeup; Kwak, Chong Hoon

    2009-05-01

    We fabricated azo dye (methylorange) doped poly vinyl alcohol (MO/PVA) thin films and measured the photoinduced birefringence (PIB) kinetics for several pump beam intensities and for various MO concentrations by using the pump-probe technique. A novel approach to explain the transient behaviors of the photoinduced anisotropy is presented by employing an empirical stretched exponential time response in the course of the trans-cis-trans photoisomerization of azo molecules and is compared with the experimental data, showing excellent agreement. The stretched exponent is estimated to be β = 0.34 ± 0.04, revealing amorphous nature of the MO/PVA system.

  10. Qsars for photoinduced toxicity: 1. acute lethality of polycyclic aromatic hydrocarbons to daphnia magna'

    SciTech Connect

    Mekenyan, O.G.; Ankley, G.T.; Veith, G.D.; Call, D.J.

    1994-01-01

    Research with a variety of aquatic species has shown that while polycyclic aromatic hydrocarbons (PAHs) are generally not acutely toxic in conventional laboratory tests, many are extremely toxic in the presence of sunlight. In an effort to develop a model for predicting which PAHs may exhibit photo-induced toxicity, Newsted and Giesy (1987) reported a parabolic relationship between the toxicity and the energy of the triplet state of a variety of PAHs. The authors have reexamined these data and propose a more mechanistic explanation for the prediction of photo-induced PAH toxicity. They sought a molecular descriptor which could be computed from structure rather than measured empirically.

  11. Interactions of amiodarone with model membranes and amiodarone-photoinduced peroxidation of lipids.

    PubMed

    Sautereau, A M; Tournaire, C; Suares, M; Tocanne, J F; Paillous, N

    1992-06-23

    The potent antiarrhythmic drug, amiodarone (AMIO) exhibits phototoxicity, which is thought to be related to its interaction with biological membranes. We report here a spectroscopic study of the interactions of this drug with phosphatidylglycerol (PG) and phosphatidylcholine (PC) liposomes used as membrane model systems. A linear increase in absorbance at 300 nm was observed with increasing addition of AMIO to dimyristoyl-DL-PC (DMPC) liposomes over all the drugs-lipid molar ratio (Ri)s tested. In contrast, in the dimyristoyl-DL-PG (DMPG) liposomes, there was a dramatic increase in absorbance at values of Ri above unity. Light scattering by DMPG liposomes at 350 nm increased with increasing AMIO concentration up to a Ri = 1, and then decreased with increasing drug concentration. Such changes were not observed with the DMPC liposomes. Moreover, addition of AMIO changed the fluorescence polarization rate of 1,6-diphenyl 1,3,5-hexatriene embedded in these liposomes. It reduced the rate below the phase transition temperature (Tt) of the lipid, but increased it above this temperature. These effects on the lipidic phases observed at low Ri were more pronounced on the DMPG than on the DMPC liposomes. The strong interactions of AMIO with phospholipids, especially the acidic ones, were confirmed by liposome size determinations. All these data strongly suggest that the drug was incorporated in the core of the lipid bilayers. Such a penetration would favor a drug-photoinduced peroxidation of lipids. Indeed, UV irradiation of AMIO-DOPG mixtures led to the disappearance of the unsaturated fatty acids of phospholipids, checked by gas chromatography measurements, which was correlated with the amount of oxygen consumed. This showed that AMIO did photosensitize phospholipid peroxidation.

  12. Photoinduced charge recombination in dipolar D-A-A photonic liquid crystal polymorphs.

    PubMed

    Mazza, Mercedes M A; Yamazaki, Shiori; Mai, Dieu X; Padgaonkar, Suyog; Peurifoy, Samuel; Goncalves, Ariane; Wu, Yi-Lin; Hu, Qiaoyu; Scott, Amy M

    2017-02-08

    A hexylalkoxy dipolar D-A-A molecule [7-(4-N,N-(bis(4-hexyloxyphenyl)amino)phenyl)-2,1,3-(benzothia-diazol-4-yl)methylene]propane-dinitrile, (C6-TPA-BT-CN) has been synthesized and the photophysics studied via femtosecond transient absorption spectroscopy (FsTA) in toluene and in amorphous and liquid crystalline spherulite thin films. Two spherulite macromolecular crystalline phases (banded, and non-banded) were observed through concentration dependent, solution processing techniques and are birefringent with a negative sign of elongation. A dramatic change in the electronic absorption from blue in amorphous films to green in spherulites was observed, and the molecular orientation was determined through the combined analysis of polarized light microscopy, X-ray diffraction, and scanning electron microscopy. FsTA was performed on amorphous films and show complex charge recombination dynamics, and a Stark effect, characterized from the combined TPA+˙ and [BT-CN]-˙ spectroscopic signatures at 450 nm and 510 nm and identified through spectroelectrochemistry. Radical cation dynamics of TPA+˙ was observed selectively at 750 nm with >503.3 ps (18%) recombination kinetics resulting in a rather significant yield of free charge carriers in amorphous films and consistent with previous reports on energetically disordered blend films. However, photoexcitation on large, non-banded spherulites areas (>250 μm) reveal average monoexponential charge recombination lifetimes of 169.2 ps from delocalized states similar to those observed in amorphous films and are 5× longer-lived than previous reports [Chang et al., J. Am. Chem. Soc., 2013, 135, 8790] of a related methyl-DPAT-BT-CN whose amorphous thin films were prepared through vapor deposition. Thus, the correlation between the microstructure of the blend film and the photoinduced radical pair dynamics described here is critical for developing a fundamental understanding of how dipolar states contribute to the charge carrier

  13. Irving Langmuir Prize Talk: Single-Molecule Fluorescence Imaging: Nanoscale Emitters with Photoinduced Switching Enable Superresolution.

    NASA Astrophysics Data System (ADS)

    Moerner, W. E.

    2009-03-01

    In the two decades since the first optical detection and spectroscopy of a single molecule in a solid (Phys. Rev. Lett. 62, 2535 (1989)), much has been learned about the ability of single molecules to probe local nanoenvironments and individual behavior in biological and nonbiological materials in the absence of ensemble averaging that can obscure heterogeneity. The early years concentrated on high-resolution spectroscopy in solids, which provided observations of lifetime-limited spectra, optical saturation, spectral diffusion, optical switching, vibrational spectra, and magnetic resonance of a single molecular spin. In the mid-1990's, much of the field moved to room temperature, where a wide variety of biophysical effects were subsequently explored, but it is worth noting that several features from the low-temperature studies have analogs at high temperature. For example, in our first studies of yellow-emitting variants of green fluorescent protein (EYFP) in the water-filled pores of a gel (Nature 388, 355 (1997)), optically induced switching of the emission was observed, a room-temperature analog of the earlier low-temperature behavior. Because each single fluorophore acts a light source roughly 1 nm in size, microscopic imaging of individual fluorophores leads naturally to superlocalization, or determination of the position of the molecule with precision beyond the optical diffraction limit, simply by digitization of the point-spread function from the single emitter. Recent work has allowed measurement of the shape of single filaments in a living cell simply by allowing a single molecule to move through the filament (PNAS 103, 10929 (2006)). The additional use of photoinduced control of single-molecule emission allows imaging beyond the diffraction limit (superresolution) by several novel approaches proposed by different researchers. For example, using photoswitchable EYFP, a novel protein superstructure can now be directly imaged in a living bacterial cell at

  14. Photoinduced axial ligation and deligation dynamics of nonplanar nickel dodecaarylporphyrins.

    PubMed

    Retsek, Jennifer L; Drain, Charles Michael; Kirmaier, Christine; Nurco, Daniel J; Medforth, Craig J; Smith, Kevin M; Sazanovich, Igor V; Chirvony, Vladimir S; Fajer, Jack; Holten, Dewey

    2003-08-13

    and open new avenues for exploring photoinduced ligand association and dissociation behavior.

  15. Hetero-cycloreversions mediated by photoinduced electron transfer.

    PubMed

    Pérez-Ruiz, Raúl; Jiménez, M Consuelo; Miranda, Miguel A

    2014-04-15

    Discovered more than eight decades ago, the Diels-Alder (DA) cycloaddition (CA) remains one of the most versatile tools in synthetic organic chemistry. Hetero-DA processes are powerful methods for the synthesis of densely functionalized six-membered heterocycles, ubiquitous substructures found in natural products and bioactive compounds. These reactions frequently employ azadienes and oxadienes, but only a few groups have reported DA processes with thiadienes. The electron transfer (ET) version of the DA reaction, though less investigated, has emerged as a subject of increasing interest. In the last two decades, researchers have paid closer attention to radical ionic hetero-cycloreversions, mainly in connection with their possible involvement in the repair of pyrimidine(6-4)pyrimidone photolesions in DNA by photolyases. In biological systems, these reactions likely occur through a reductive photosensitization mechanism. In addition, photooxidation can lead to cycloreversion (CR) reactions, and researchers can exploit this strategy for DNA repair therapies. In this Account, we discuss electron-transfer (ET) mediated hetero-CR reactions. We focus on the oxidative and reductive ET splitting of oxetanes, azetidines, and thietanes. Photoinduced electron transfer facilitates the splitting of a variety of four-membered heterocycles. In this context, researchers have commonly examined oxetanes, both experimentally and theoretically. Although a few studies have reported the cycloreversion of azetidines and thietanes carried out under electron transfer conditions, the number of examples remains limited. In general, the cleavage of the ionized four-membered rings appears to occur via a nonconcerted two-step mechanism. The trapping of the intermediate 1,4-radical ions and transient absorption spectroscopy data support this hypothesis, and it explains the observed loss of stereochemistry in the products. In the initial step, either C-C or C-X bond breaking may occur, and the

  16. Revising Intramolecular Photoinduced Electron Transfer (PET) from First-Principles.

    PubMed

    Escudero, Daniel

    2016-09-20

    Photoinduced electron transfer (PET) plays relevant roles in many areas of chemistry, including charge separation processes in photovoltaics, natural and artificial photosynthesis, and photoluminescence sensors and switches. As in many other photochemical scenarios, the structural and energetic factors play relevant roles in determining the rates and efficiencies of PET and its competitive photodeactivation processes. Particularly, in the field of fluorescent sensors and switches, intramolecular PET is believed (in many cases without compelling experimental proof) to be responsible of the quench of fluorescence. There is an increasing experimental interest in fluorophore's molecular design and on achieving optimal excitation/emission spectra, excitation coefficients, and fluorescence quantum yields (importantly for bioimaging purposes), but less efforts are devoted to fundamental mechanistic studies. In this Account, I revise the origins of the fluorescence quenching in some of these systems with state-of-the-art quantum chemical tools. These studies go beyond the common strategy of analyzing frontier orbital energy diagrams and performing PET thermodynamics calculations. Instead, the potential energy surfaces (PESs) of the lowest-lying excited states are explored with time-dependent density functional theory (TD-DFT) and complete active space self-consistent field (CASSCF) calculations and the radiative and nonradiative decay rates from the involved excited states are computed from first-principles using a thermal vibration correlation function formalism. With such a strategy, this work reveals the real origins of the fluorescence quenching, herein entitled as dark-state quenching. Dark states (those that do not absorb or emit light) are often elusive to experiments and thus, computational investigations can provide novel insights into the actual photodeactivation mechanisms. The success of the dark-state quenching mechanism is demonstrated for a wide variety of

  17. Spectral derivative feature coding for hyperspectral signature analysis

    NASA Astrophysics Data System (ADS)

    Chang, Chein-I.; Chakravarty, Sumit

    2006-08-01

    This paper presents a new approach to hyperspectral signature analysis, called Spectral Derivative Feature Coding (SDFC). It makes use of gradient changes in adjacent bands to characterize spectral variations so as to improve spectral discrimination and identification. In order to evaluate its performance, two binary coding methods, SPectral Analysis Manager (SPAM) and Spectral Feature-based Binary Coding (SFBC) are used to conduct comparative analysis. The experimental results demonstrate the proposed SDFC performs more effectively in capturing spectral characteristics.

  18. Energetic comparison between photoinduced electron-transfer reactions from NADH model compounds to organic and inorganic oxidants and hydride-transfer reactions from NADH model compounds to p-benzoquinone derivatives

    SciTech Connect

    Fukuzumi, S.; Koumitsu, S.; Hironaka, K.; Tanaka, T.

    1987-01-21

    Kinetic studies on photoinduced electron-transfer reactions from dihydropyridine compounds (PyH/sub 2/) as being NADH model compounds to organic and inorganic oxidants and hydride-transfer reactions from PyH/sub 2/ to p-benzoquinone derivatives (Q) in the absence and presence of Mg/sup 2 +/ ion are reported by determining over 150 rate constants. These results, combined with the values of Gibbs energy change of the photoinduced electron-transfer reactions as well as those of each step of the hydride-transfer reactions as being the e/sup -/-H/sup +/-e/sup -/ sequence, which are determined independently, revealed that the rate constants of the photoinduced electron-transfer reactions obey the Rehm-Weller-Gibbs energy relationship and that the activation barrier of the hydride-transfer reactions from PyH/sub 2/ to Q is dependent solely on the Gibbs energy changes of the initial electron transfer from PyH/sub 2/ to Q and the following proton transfer from PyH/sub 2//sup .+/ to Q/sup .-/ and thus independent of the Gibbs energy change of the final electron transfer from PyH/sup ./ to QH/sup ./. The retarding effect of Mg/sup 2 +/ ion observed on the photoinduced electron transfer and hydride-transfer reactions of PyH/sub 2/ is ascribed to the positive shifts of the redox potentials of the ground and excited states of PyH/sub 2/ due to the complex formation with Mg/sup 2 +/ ion.

  19. Photoinduced electron transfer from rail to rung within a self-assembled oligomeric porphyrin ladder

    SciTech Connect

    She, Chunxing; Lee, Suk Joong; McGarrah, James E.; Vura-Weis, Josh; Wasielewski, Michael; Chen, Hanning; Schatz, George C.; Ratner, Mark A.; Hupp, Joseph T.

    2010-01-01

    Photoinduced electron transfer in a self-assembled supramolecular ladder structure comprising oligomeric porphyrin rails and ligated dipyridyltetrazine rungs was characterized by transient absorption spectroscopy and transient direct current photoconductivity to be mainly from an oligomer (rail) to the center of a terminal tetrazine (rung), with the remaining hole being delocalized on the oligomer and subsequent charge recombination in 0.19 ns.

  20. Distance dependence in photoinduced intramolecular electron transfer. Additional remarks and calculations

    NASA Astrophysics Data System (ADS)

    Larsson, Sven; Volosov, Andrey

    1987-12-01

    Rate constants for photoinduced intramolecular electron transfer are calculated for four of the molecules studied by Hush et al. The electronic factor is obtained in quantum chemical calculations using the CNDO/S method. The results agree reasonably well with experiments for the forward reaction. Possible reasons for the disagreement for the charge recombination process are offered.

  1. EFFECT OF IRRADIANCE SPECTRA ON THE PHOTOINDUCED TOXICITY OF THREE POLYCYCLIC AROMATIC HYDROCARBONS

    EPA Science Inventory

    Photoinduced toxicity of polycyclic aromatic hydrocarbons (PAHs) is dependent on the concentration of compounds present and the dose of light received. Of the light present, only those wavelengths absorbed by the compound have the potential to initiate the photochemical events un...

  2. Photoinduced Electron Transfer from Various Aniline Derivatives to Graphene Quantum Dots.

    PubMed

    Ghosh, Tufan; Chatterjee, Swarupa; Prasad, Edamana

    2015-12-10

    The present study utilizes the luminescence nature of the graphene quantum dots (GQDs) to analyze the mechanistic aspects of the photoinduced electron transfer (PET) processes between GQDs and aniline derivatives. A systematic investigation of PET from various aniline derivatives to GQDs has been presented. Solution-processable GQDs have been synthesized from graphene oxide (GO) at 200 °C. The as-synthesized GQDs exhibit a strong green luminescence at 510 nm, upon photoexcitation at 440 nm. Various aniline derivatives (aniline, N-methylaniline, N,N'-dimethylaniline, N-ethylaniline, N,N'-diethylaniline, and N,N'-diphenylaniline) have been utilized as electron donors to probe the PET process. Results from UV-visible absorption and steady-state and time-resolve luminescence spectroscopy suggest that the GQDs interact with the aniline derivatives in the excited state, which results in a significant luminescence quenching of the GQDs. The bimolecular rate constants of the dynamic quenching have been deduced for various donor-acceptor systems, and the values are in the range of (1.06-2.68) × 10(9) M(-1) s(-1). The negative values of the free energy change of the electron transfer process suggest that PET from aniline derivatives to GQDs is feasible and could be responsible for the luminescence quenching. The PET has been confirmed by detecting radical cations for certain aniline derivatives, using a nanosecond laser flash photolysis setup. The present study shows that among the various types of graphene systems, GQDs are better candidates for understanding the mechanism of PET in graphene-based donor-acceptor systems.

  3. Electric-field modulation of photoinduced effect in phase-separated Pr0.65 (Ca0.75Sr0.25)0.35MnO3/PMN-PT heterostructure

    NASA Astrophysics Data System (ADS)

    Li, W.; Dong, X. L.; Wang, S. H.; Jin, K. X.

    2016-08-01

    In this letter, we report the photoinduced effect modulated by different electric fields in the Pr0.65 (Ca0.75Sr0.25)0.35MnO3/0.7PbMg1/3Nb2/3O3-0.3PbTiO3 heterostructure. The film exhibits a decrease in the resistance up to five orders of magnitude by enhancing applied electric fields, combined with an electric-field-induced insulator-to-metal transition. More interestingly, a reversible bistability arises in the photoinduced change in resistance at T < 80 K as the voltages are increased. The results can be attributed to the phase separation in manganites, which provides a prototype of photoelectric conversion for electric-field modulation of all-oxide heterostructures.

  4. Effect of spectral correlations on spectral switches in the diffraction of partially coherent light.

    PubMed

    Pu, Jixiong; Nemoto, Shojiro; Lü, Baida

    2003-10-01

    The subject is the spectral characteristics of partially coherent light whose spectral degree of coherence satisfies or violates the scaling law in diffraction by a circular aperture. Three kinds of spectral correlations of the incident light are considered. It is shown that no matter whether the partially coherent light satisfies or violates the scaling law, a spectral switch defined as a rapid transition of spectral shifts is always found in the diffraction field. Different spectral correlations of the incident field in the aperture result in different points at which the spectral switch occurs. With an increment in the correlations, the position at which the spectral switch takes place moves toward the point at which the phase of the center frequency component omega0 becomes singular for illumination by spatially fully coherent light. For light that satisfies the scaling law, the spectral switch is attributed to the diffraction-induced spectral changes; for partially coherent light that violates the scaling law, the spectral switch is attributed to both the diffraction-induced spectral changes and the correlation-induced spectral changes.

  5. Spectral and spread-spectral teleportation

    SciTech Connect

    Humble, Travis S.

    2010-06-15

    We report how quantum information encoded into the spectral degree of freedom of a single-photon state may be teleported using a finite spectrally entangled biphoton state. We further demonstrate how the bandwidth of the teleported wave form can be controllably and coherently dilated using a spread-spectral variant of teleportation. We calculate analytical expressions for the fidelities of spectral and spread-spectral teleportation when complex-valued Gaussian states are transferred using a proposed experimental approach. Finally, we discuss the utility of these techniques for integrating broad-bandwidth photonic qubits with narrow-bandwidth receivers in quantum communication systems.

  6. Photo-induced current amplification in L-histidine modified nanochannels based on a highly charged photoacid in solution.

    PubMed

    Zhang, Minghui; Meng, Zheyi; Zhai, Jin; Jiang, Lei

    2013-03-21

    By UV light irradiation, we can adjust the charge of bistable photoacid molecules reversibly, so that photo-induced current amplification can be obtained, which offers a way to control nanochannels by turning the UV light on and off, alternately.

  7. Photo-induced oxidation and amorphization of trigonal tellurium: A means to engineer hybrid nanostructures and explore glass structure under spatial confinement

    SciTech Connect

    Vasileiadis, Thomas; Yannopoulos, Spyros N.

    2014-09-14

    Controlled photo-induced oxidation and amorphization of elemental trigonal tellurium are achieved by laser irradiation at optical wavelengths. These processes are monitored in situ by time-resolved Raman scattering and ex situ by electron microscopies. Ultrathin TeO₂ films form on Te surfaces, as a result of irradiation, with an interface layer of amorphous Te intervening between them. It is shown that irradiation, apart from enabling the controllable transformation of bulk Te to one-dimensional nanostructures, such as Te nanotubes and hybrid core-Te/sheath-TeO₂ nanowires, causes also a series of light-driven (athermal) phase transitions involving the crystallization of the amorphous TeO₂ layers and its transformation to a multiplicity of crystalline phases including the γ-, β-, and α-TeO₂ crystalline phases. The kinetics of the above photo-induced processes is investigated by Raman scattering at various laser fluences revealing exponential and non-exponential kinetics at low and high fluence, respectively. In addition, the formation of ultrathin (less than 10 nm) layers of amorphous TeO₂ offers the possibility to explore structural transitions in 2D glasses by observing changes in the short- and medium-range structural order induced by spatial confinement.

  8. Label-free colorimetric detection of biological thiols based on target-triggered inhibition of photoinduced formation of AuNPs

    NASA Astrophysics Data System (ADS)

    Lim Jung, Ye; Park, Jung Hun; Kim, Moon Il; Park, Hyun Gyu

    2016-02-01

    A label-free colorimetric method for the detection of biological thiols (biothiols) was developed. This method is based on prevention of the photoinduced reduction of auric ions (Au(III)) in the presence of amino acids (acting as a reducing agent) by biothiols; the photoinduced reduction is inhibited due to the strong interaction of the biothiols with Au(III). In this method, the sample was first incubated in an assay solution containing Au(III) and threonine; the sample solution was then exposed to 254 nm UV light. For samples without biothiols, this process led to the photoreduction of Au(III) followed by growth of gold nanoparticles accompanied by the visually detectable development of a red coloration typified by an absorption peak at ca 530 nm. Conversely, in the presence of biothiols, reduction of Au(III) to Au(0) was prevented by entrapment of Au(III) within the biothiols via the thiol group. The solution thus remained colorless even after UV irradiation, which was used as an indicator of the presence of biothiols. Using this strategy, biothiols were very conveniently analyzed by monitoring color changes of the samples with the naked eye or a UV-vis spectrometer. The strategy based on this interesting phenomenon exhibited high selectivity toward biothiols over common amino acids and was successfully employed for reliable quantification of biothiols present in human plasma, demonstrating its great potential for clinical applications.

  9. Acute photo-induced toxicity and toxicokinetics of single compounds and mixtures of polycyclic aromatic hydrocarbons in zebrafish.

    PubMed

    Willis, Alison M; Oris, James T

    2014-09-01

    The present study examined photo-induced toxicity and toxicokinetics for acute exposure to selected polycyclic aromatic hydrocarbons (PAHs) in zebrafish. Photo-enhanced toxicity from co-exposure to ultraviolet (UV) radiation and PAHs enhanced the toxicity and exhibited toxic effects at PAH concentrations orders of magnitude below effects observed in the absence of UV. Because environmental exposure to PAHs is usually in the form of complex mixtures, the present study examined the photo-induced toxicity of both single compounds and mixtures of PAHs. In a sensitive larval life stage of zebrafish, acute photo-induced median lethal concentrations (LC50s) were derived for 4 PAHs (anthracene, pyrene, carbazole, and phenanthrene) to examine the hypothesis that phototoxic (anthracene and pyrene) and nonphototoxic (carbazole and phenanthrene) pathways of mixtures could be predicted from single exposures. Anthracene and pyrene were phototoxic as predicted; however, carbazole exhibited moderate photo-induced toxicity and phenanthrene exhibited weak photo-induced toxicity. The toxicity of each chemical alone was used to compare the toxicity of mixtures in binary, tertiary, and quaternary combinations of these PAHs, and a predictive model for environmental mixtures was generated. The results indicated that the acute toxicity of PAH mixtures was additive in phototoxic scenarios, regardless of the magnitude of photo-enhancement. Based on PAH concentrations found in water and circumstances of high UV dose to aquatic systems, there exists potential risk of photo-induced toxicity to aquatic organisms.

  10. Quantum Spectral Symmetries

    NASA Astrophysics Data System (ADS)

    Hamhalter, Jan; Turilova, Ekaterina

    2017-02-01

    Quantum symmetries of spectral lattices are studied. Basic properties of spectral order on A W ∗-algebras are summarized. Connection between projection and spectral automorphisms is clarified by showing that, under mild conditions, any spectral automorphism is a composition of function calculus and Jordan ∗-automorphism. Complete description of quantum spectral symmetries on Type I and Type II A W ∗-factors are completely described.

  11. Photoinduced intramolecular charge transfer in push-pull polyenes: effects of solvation, electron-donor group, and polyenic chain length.

    PubMed

    Akemann, Walther; Laage, Damien; Plaza, Pascal; Martin, Monique M; Blanchard-Desce, Mireille

    2008-01-17

    Subpicosecond absorption spectroscopy is used to characterize the primary photoinduced processes in a class of push-pull polyenes bearing a julolidine end group as the electron donor and a diethylthiobarbituric acid end group as the electron acceptor. The excited-state decay time and relaxation pathway have been studied for four polyenes of increasing chain length (n = 2-5 double bonds) in aprotic solvents of different solvation time, polarity, and viscosity. Intramolecular charge transfer (ICT) leading to a transient state of cyanine-like structure (fully conjugated with no bond length alternation) is observed in all polar solvents at a solvent dependent rate, but the reaction is not observed in cyclohexane, a nonpolar solvent. In polar solvents, the reaction time increases with the average solvation time but remains slightly larger, except in the viscous solvent triacetin. These facts are interpreted as an indication that both solvent reorganization and internal restructuring are involved in the ICT-state formation. The observed photodynamics resemble those we previously found for another class of polyenes bearing a dibutylaniline group as the donor, including a similar charge-transfer rate in spite of the larger electron donor character of the julolidine group. This observation brings further support to the proposal that an intramolecular coordinate is involved in the charge-transfer reaction, possibly a torsional motion of the donor end group. On the other hand, relaxation of the ICT state leads to cis-trans isomerization or crossing to the triplet state, depending on the length of the polyenic chain. In dioxane, tetrahydrofuran, and triacetin, the ICT state of the shorter chains (n = 2, 3) relaxes to the isomer with a viscosity-dependent rate, while that of the longer ones (n = 4, 5) leads to the triplet state with a viscosity-independent rate, as expected. In acetonitrile, the ICT-state lifetime is generally much shorter. A change from photoisomerization to

  12. A bifunctional amorphous polymer exhibiting equal linear and circular photoinduced birefringences.

    PubMed

    Royes, Jorge; Provenzano, Clementina; Pagliusi, Pasquale; Tejedor, Rosa M; Piñol, Milagros; Oriol, Luis

    2014-11-01

    The large and reversible photoinduced linear and circular birefringences in azo-compounds are at the basis of the interest in these materials, which are potentially useful for several applications. Since the onset of the linear and circular anisotropies relies on orientational processes, which typically occur on the molecular and supramolecular length scale, respectively, a circular birefringence at least one order of magnitude lower than the linear one is usually observed. Here, the synthesis and characterization of an amorphous polymer with a dimeric repeating unit containing a cyanoazobenzene and a cyanobiphenyl moiety are reported, in which identical optical linear and circular birefringences are induced for proper light dose and ellipticity. A pump-probe technique and an analytical method based on the Stokes-Mueller formalism are used to investigate the photoinduced effects and to evaluate the anisotropies. The peculiar photoresponse of the polymer makes it a good candidate for applications in smart functional devices.

  13. Enhanced diffraction properties of photoinduced gratings in nematic liquid crystals doped with Disperse Red 1.

    PubMed

    Li, Hongjing; Wang, Jianhao; Wang, Changshun; Zeng, Pengfei; Pan, Yujia; Yang, Yifei

    2016-01-01

    Diffraction properties of photoinduced gratings recorded by overlapping two coherent beams at 532 nm in nematic liquid crystals doped with Disperse Red 1 were investigated with a probe beam at 632.8 nm. The grating was formed due to the alignment of dye molecules that leaded to the reorientation of the liquid crystal phase. The diffraction efficiency of the photoinduced grating was found to increase rapidly when the sample temperature was close to the clearing point in the nematic phase and a nearly 30-fold enhancement of the first-order diffraction efficiency was obtained. The pretransitional enhancement of the diffraction efficiency was discussed in terms of the reorientation of liquid crystals, optical nonlinearity effects and the onset of critical opalescence near the nematic-isotropic phase transition. Moreover, a peak shift of diffraction efficiency towards the lower temperature was observed with the increase of recording light intensity, which was attributed to laser induced photochemical disordering.

  14. Genetically engineered photoinducible homodimerization system with improved dimer-forming efficiency.

    PubMed

    Nihongaki, Yuta; Suzuki, Hideyuki; Kawano, Fuun; Sato, Moritoshi

    2014-03-21

    Vivid (VVD) is a photoreceptor derived from Neurospora Crassa that rapidly forms a homodimer in response to blue light. Although VVD has several advantages over other photoreceptors as photoinducible homodimerization system, VVD has a critical limitation in its low dimer-forming efficiency. To overcome this limitation of wild-type VVD, here we conduct site-directed saturation mutagenesis in the homodimer interface of VVD. We have found that the Ile52Cys mutation of VVD (VVD-52C) substantially improves its homodimer-forming efficiency up to 180%. We have demonstrated the utility of VVD-52C for making a light-inducible gene expression system more robust. In addition, using VVD-52C, we have developed photoactivatable caspase-9, which enables optical control of apoptosis of mammalian cells. The present genetically engineered photoinducible homodimerization system can provide a powerful tool to optically control a broad range of molecular processes in the cell.

  15. Enhanced diffraction properties of photoinduced gratings in nematic liquid crystals doped with Disperse Red 1

    PubMed Central

    LI, Hongjing; WANG, Jianhao; WANG, Changshun; ZENG, Pengfei; PAN, Yujia; YANG, Yifei

    2016-01-01

    Diffraction properties of photoinduced gratings recorded by overlapping two coherent beams at 532 nm in nematic liquid crystals doped with Disperse Red 1 were investigated with a probe beam at 632.8 nm. The grating was formed due to the alignment of dye molecules that leaded to the reorientation of the liquid crystal phase. The diffraction efficiency of the photoinduced grating was found to increase rapidly when the sample temperature was close to the clearing point in the nematic phase and a nearly 30-fold enhancement of the first-order diffraction efficiency was obtained. The pretransitional enhancement of the diffraction efficiency was discussed in terms of the reorientation of liquid crystals, optical nonlinearity effects and the onset of critical opalescence near the nematic-isotropic phase transition. Moreover, a peak shift of diffraction efficiency towards the lower temperature was observed with the increase of recording light intensity, which was attributed to laser induced photochemical disordering. PMID:27725471

  16. Photo-induced Modulation Doping in Graphene/Boron nitride Heterostructures

    NASA Astrophysics Data System (ADS)

    Velasco, Jairo, Jr.; Ju, Long; Hwang, Edwin; Kahn, Salman; Nosiglia, Casey; Tsai, Hsin-Zon; Yang, Wei; Zhang, Guangyu; Taniguchi, Takashi; Watanabe, Kenji; Zhang, Yuanbo; Crommie, Michael; Zettl, Alex; Wang, Feng

    2014-03-01

    Van der Waals heterostructures (VDH) provide an exciting new platform for materials engineering, where a variety of layered materials with different electrical, optical and mechanical responses can be stacked together to enable new physics and novel functionalities. We report an emerging optoelectronic phenomenon (i.e. photo-induced modulation doping) in the graphene-boron nitride VDH (G/BN heterostructure). We find it enables flexible and repeatable writing and erasing of charge doping in graphene with optical light. We show that the photo-induced modulation doping maintains the remarkable carrier mobility of the G/BN heterostructure, and it can be used to generate spatially varying doping profiles like pn junctions. Our work contributes towards understanding light matter interactions in VDHs, and introduces a simple technique for creating inhomogeneous doping in high mobility graphene devices. J. Velasco Jr. acknowledges support from UC President's Postdoctoral Fellowship.

  17. Eigenmodes of a quartz tuning fork and their application to photoinduced force microscopy

    NASA Astrophysics Data System (ADS)

    Kim, Bongsu; Jahng, Junghoon; Khan, Ryan Muhammad; Park, Sung; Potma, Eric O.

    2017-02-01

    We examine the mechanical eigenmodes of a quartz tuning fork (QTF) for the purpose of facilitating its use as a probe for multifrequency atomic force microscopy (AFM). We perform simulations based on the three-dimensional finite element method and compare the observed motions of the beams with experimentally measured resonance frequencies of two QTF systems. The comparison enabled us to assign the first seven asymmetric eigenmodes of the QTF. We also find that a modified version of single beam theory can be used to guide the assignment of mechanical eigenmodes of QTFs. The usefulness of the QTF for multifrequency AFM measurements is demonstrated through photoinduced force microscopy measurements. By using the QTF in different configurations, we show that the vectorial components of the photoinduced force can be independently assessed and that lateral forces can be probed in true noncontact mode.

  18. A dinuclear Ru(II) complex capable of photoinduced ligand exchange at both metal centers.

    PubMed

    Albani, B A; Peña, B; Saha, S; White, J K; Schaeffer, A M; Dunbar, K R; Turro, C

    2015-11-28

    {[Ru(CH3CN)3]2(tppz)}(4+) (tppz = tetra-2-pyridylpyrazine) undergoes photoinduced CH3CN exchange with λirr ≥ 610 nm in H2O. In contrast, cis-{[Ru(tpy)(L)]2(bpm)}(4+) (tpy = 2,2':6',2''-terpyridine, bpm = 2,2'-bipyrimidine, L = CH3CN) is not reactive, but the complex with L = DMSO is photoactive. These complexes are potentially useful for the release of multiply caged drugs.

  19. Stochastic model for photoinduced surface relief grating formation through molecular transport in polymer films.

    SciTech Connect

    Juan, M.; Plain, J.; Bachelot, R.; Royer, P.; Gray, S. K.; Wiederrecht, G. P.; Univ. de Technologie de Troyes

    2008-09-01

    We use a stochastic model to study photoinduced surface relief grating (SRG) formation due to molecular transport in azobenzene polymer films. The model is shown to reproduce the essential experimental features of SRG formation. In particular, it predicts SRG formation under both p and s polarizations, and the double peaked topographies that can occur at early times of the process. The evolving molecular positions and orientations during exposure are also followed, providing a useful mechanistic picture of SRG dynamics.

  20. Stochastic model for photoinduced surface relief grating formation through molecular transport in polymer films

    SciTech Connect

    Juan, M. L.; Plain, J.; Bachelot, R.; Royer, P.; Gray, S. K.; Wiederrecht, G. P.

    2008-10-13

    We use a stochastic model to study photoinduced surface relief grating (SRG) formation due to molecular transport in azobenzene polymer films. The model is shown to reproduce the essential experimental features of SRG formation. In particular, it predicts SRG formation under both p and s polarizations, and the double peaked topographies that can occur at early times of the process. The evolving molecular positions and orientations during exposure are also followed, providing a useful mechanistic picture of SRG dynamics.

  1. Procedure for quantitative determination of effectiveness of photoinduced destruction of malignant tumors

    NASA Astrophysics Data System (ADS)

    Bizyuk, S. A.; Istomin, Yu. P.; Dzhagarov, B. M.

    2006-07-01

    We have developed a procedure for analysis of the functional status of blood vessels in tumor tissues using computer-assisted color scanning of tumor slices and also for a quantitative assessment of the effectiveness of photoinduced destruction of tumor tissues in animal experiments. Its major advantage is direct determination of the size of the tumor necrosis zone. The procedure has been tested in an experiment on three strains of malignant tumors with different morphologies.

  2. Monte-Carlo simulations of photoinduced fluorescence enhancement in semiconductor quantum dot arrays

    NASA Astrophysics Data System (ADS)

    Maenosono, Shinya

    2005-03-01

    Photoinduced fluorescence enhancement (PFE) in semiconductor quantum dot (QD) arrays is simulated by a Monte-Carlo method based on the distributed tunneling model. PFE, a property of a QD ensemble, is directly related to the blinking behavior of single QDs. The origin of PFE is attributed not to an increase in the emission intensity during the 'on' period, but to the prolongation of average 'on' time.

  3. Time-Resolved Studies of Photoinduced Birefringence in Azobenzene Dye-Doped Polymer Films

    DTIC Science & Technology

    2008-09-23

    Here we report on transient photoinduced birefrin- gence ( PIB ) measurements on several azo dye films using a nanosecond laser source with a 20ns time re...Our results show the response time of PIB to be sys- tematically related to the size of the lowest optical transition energy. Furthermore, our results...suggest that PIB effects can be used to discriminate between0003-6935/08/285074-04$15.00/0 © 2008 Optical Society of America 5074 APPLIED OPTICS / Vol

  4. Electron Donor-Acceptor Quenching and Photoinduced Electron Transfer for Coumarin Dyes.

    DTIC Science & Technology

    1983-10-31

    Mechanism of cousarin photodegradation . Ithe behavior of eoiuma dyes is water ad In aqueous detergent media,. and the effsects of medism aud, additives on...D-i36 345 ELECTRON DONOR-ACCEPTOR UENCHING AND PHOTOINDUCED i/i Ai ELECTRON TRANSFER FOR COUMARIN DYES (U) BOSTON UNIY MR DEPT OF CHEMISTRY G JONES...TYPE OF REPORT & PEIOD COVERED Electron Donor-acceptor Quenching and Photo- Technical, 1/1/82-10/31/82 induced Electron Transfer for Coumarin Dyes S

  5. 8-Methoxypsoralen photoinduced plasmid-chromosome recombination in Saccharomyces cerevisiae using a centromeric vector.

    PubMed Central

    Meira, L B; Henriques, J A; Magaña-Schwencke, N

    1995-01-01

    The characterization of a new system to study the induction of plasmid-chromosome recombination is described. Single-stranded and double-stranded centromeric vectors bearing 8-methoxypsoralen photoinduced lesions were used to transform a wild-type yeast strain bearing the leu2-3,112 marker. Using the SSCP methodology and DNA sequencing, it was demonstrated that repair of the lesions in plasmid DNA was mainly due to conversion of the chromosomal allele to the plasmid DNA. Images PMID:7784218

  6. Neuronal regulation of photo-induced pineal photoreceptor proteins in carp Catla catla.

    PubMed

    Seth, Mohua; Maitra, Saumen Kumar

    2010-08-01

    In the present in vitro study on the pineal in carp Catla catla, specific agonist and antagonists of receptors for different neuronal signals and regulators of intra-cellular Ca(++) and cAMP were used to gather basic information on the neuronal signal transduction cascade mechanisms in the photo-induced expression of rod-like opsin and alpha-transducin-like proteins in any fish pineal. Western-blot analysis followed by quantitative analysis of respective immunoblot data for both the proteins revealed that photo-induced expression of each protein was stimulated by cholinergic (both nicotinic and muscarinic) agonists and a dopaminergic antagonist, inhibited by both cholinergic antagonists and a dopaminergic agonist, but not affected by any agonists or antagonists of adrenergic (alpha(1), alpha(2) and beta(1)) receptors. Moreover, expression of each protein was stimulated by voltage gated L type calcium channel blocker, adenylate cyclase inhibitor and phosphodiesterase activator; but suppressed by the activators of both calcium channel and adenylate cyclase, and by phosphodiesterase inhibitor. Collectively, we report for the first time that both cholinergic and dopaminergic signals play an important, though antagonistic, role in the photo-induced expression of photoreceptor proteins in the fish pineal through activation of a signal transduction pathway in which both calcium and cAMP may act as the intracellular messengers.

  7. Highly active ppm level organic copper catalyzed photo-induced ICAR ATRP of methyl methacrylate.

    PubMed

    Jiang, Xiaowu; Wu, Jian; Zhang, Lifen; Cheng, Zhenping; Zhu, Xiulin

    2014-11-01

    A novel photo-induced homogeneous atom transfer radical polymerization (ATRP) system is constructed using an organic copper salt (Cu(SC(S)N(C2 H5 )2 )2 ) as a photo-induced catalyst at 30 °C. Herein, N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA) is used as a ligand, ethyl 2-bromophenylacetate (EBPA) as an ATRP initiator, and (2,4,6-trimethylbenzoyl) diphenylphosphine oxide (TPO) as a photo-induced radical initiator to establish an ICAR (initiators for continuous activator regeneration) ATRP using methyl methacrylate (MMA) as a modal monomer. The effect of the concentration of the organic copper on the polymerization is investigated in detail. It is found that well-controlled polymerization can be obtained even with the amount of (Cu(SC(S)N(C2 H5 )2 )2 decreasing to a 1.56 ppm level, with the molecular weight of the resultant polymers increasing linearly with monomer conversion while maintaining a narrow molecular weight distribution (M¯w/M¯n < 1.3).

  8. Photoinduced Oxidative DNA Damage Revealed by an Agarose Gel Nicking Assay: A Biophysical Chemistry Laboratory Experiment

    NASA Astrophysics Data System (ADS)

    Shafirovich, Vladimir; Singh, Carolyn; Geacintov, Nicholas E.

    2003-11-01

    Oxidative damage of DNA molecules associated with electron-transfer reactions is an important phenomenon in living cells, which can lead to mutations and contribute to carcinogenesis and the aging processes. This article describes the design of several simple experiments to explore DNA damage initiated by photoinduced electron-transfer reactions sensitized by the acridine derivative, proflavine (PF). A supercoiled DNA agarose gel nicking assay is employed as a sensitive probe of DNA strand cleavage. A low-cost experimental and computer-interfaced imaging apparatus is described allowing for the digital recording and analysis of the gel electrophoresis results. The first experiment describes the formation of direct strand breaks in double-stranded DNA induced by photoexcitation of the intercalated PF molecules. The second experiment demonstrates that the addition of the well-known electron acceptor, methylviologen, gives rise to a significant enhancement of the photochemical DNA strand cleavage effect. This occurs by an electron transfer step to methylviologen that renders the inital photoinduced charge separation between photoexcited PF and DNA irreversible. The third experiment demonstrates that the action spectrum of the DNA photocleavage matches the absorption spectrum of DNA-bound, intercalated PF molecules, which differs from that of free PF molecules. This result demonstrates that the photoinduced DNA strand cleavage is initiated by intercalated rather than free PF molecules.

  9. Phase diagram of the ultrafast photoinduced insulator-metal transition in vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Cocker, T. L.; Titova, L. V.; Fourmaux, S.; Holloway, G.; Bandulet, H.-C.; Brassard, D.; Kieffer, J.-C.; El Khakani, M. A.; Hegmann, F. A.

    2012-04-01

    We use time-resolved terahertz spectroscopy to probe the ultrafast dynamics of the insulator-metal phase transition induced by femtosecond laser pulses in a nanogranular vanadium dioxide (VO2) film. Based on the observed thresholds for characteristic transient terahertz dynamics, a phase diagram of critical pump fluence versus temperature for the insulator-metal phase transition in VO2 is established for the first time over a broad range of temperatures down to 17 K. We find that both Mott and Peierls mechanisms are present in the insulating state and that the photoinduced transition is nonthermal. We propose a critical-threshold model for the ultrafast photoinduced transition based on a critical density of electrons and a critical density of coherently excited phonons necessary for the structural transition to the metallic state. As a result, evidence is found at low temperatures for an intermediate metallic state wherein the Mott state is melted but the Peierls distortion remains intact, consistent with recent theoretical predictions. Finally, the observed terahertz conductivity dynamics above the photoinduced transition threshold reveal nucleation and growth of metallic nanodomains over picosecond time scales.

  10. Photo-induced toxicity of Deepwater Horizon slick oil to blue crab (Callinectes sapidus) larvae.

    PubMed

    Alloy, Matthew M; Boube, Idrissa; Griffitt, Robert J; Oris, James T; Roberts, Aaron P

    2015-09-01

    The 2010 Deepwater Horizon oil spill resulted in the accidental release of approximately 700 million L of crude oil into the Gulf of Mexico. Photo-induced toxicity after co-exposure to ultraviolet (UV) radiation is 1 mechanism by which polycyclic aromatic hydrocarbons (PAHs) from oil spills may exert toxicity. Blue crab are an important commercial and ecological resource in the Gulf of Mexico, and their largely transparent larvae may make them sensitive to PAH photo-induced toxicity. The goal of the present study was to examine the sensitivity of early lifestage blue crab (Callinectes sapidus) zoea to slick oil collected during the Deepwater Horizon spill. Blue crab zoea were exposed to 1 of several dilutions of water accommodated fractions from 1 of 2 sources of oil and gradations of natural sunlight in a factorial design. Two 7-h solar exposures were carried out with a recovery period (dark) in between. Survival was found to be UV- and PAH-dependent. Toxicity was observed within the range of surface PAH concentrations reported in the Gulf of Mexico during the Deepwater Horizon spill. These findings indicate that early lifestage blue crab are sensitive to photo-induced toxicity from Deepwater Horizon slick oil.

  11. Supramolecular photomagnetic materials: photoinduced dimerization of ferrocene-based polychlorotriphenylmethyl radicals.

    PubMed

    Ratera, Imma; Ruiz-Molina, Daniel; Vidal-Gancedo, José; Novoa, Juan J; Wurst, Klaus; Letard, Jean-François; Rovira, Concepció; Veciana, Jaume

    2004-02-06

    New ferrocenyl Schiff-base polychlorotriphenylmethyl radicals have been synthesized and characterized. The imino group of one such radical undergoes an irreversible trans to cis structural isomerization induced by light. Such photoinduced isomerization has been monitored by UV/Vis and ESR spectroscopy and also monitored by HPLC. ESR frozen solution experiments at low temperature revealed that the cis isomer dimerizes, showing a strong antiferromagnetic interaction. Although numerous photochromic supramolecular systems have been described, such a photoinduced self-assembly process represents the first example of a one-way photoswitchable magnetic system in which a conversion between a doublet and a singlet ground state species is promoted by a photoinduced dimerization process driven by the formation of hydrogen bonds. DFT calculations on the minimized structure and on the rotational barriers have been performed to establish the origin of such behavior. The effect of the substituents and the media polarity on the photoisomerization of this imine chromophore have also been studied. It has been observed that the efficiency of the process is markedly dependent on the presence and characteristics of electron-donor and electron-acceptor substituents of the ferrocenyl Schiff-base polychlorotriphenylmethyl radicals as well as on the polarity of the solvent.

  12. Spectral imaging of the human ocular fundus

    NASA Astrophysics Data System (ADS)

    Truitt, Paul Wiley

    Introduction. The objective of this work was to demonstrate a high spectral and spatial resolution fundus imager and to assess its utility in visualizing and characterizing normal anatomical and pathological tissue classes in the human ocular fundus. The ocular fundus (posterior portion of the eye) affords a unique opportunity to directly observe neural and vascular tissue in vivo. Many ocular and systemic diseases manifest changes in the normal fundus anatomy. Current examination techniques are not optimized to detect changes prior to the formation of damaging lesions. Spectral imaging may allow visualization of disease states before the onset of traditional clinical signs. Normal tissue in the eye has distinct spectral characteristics determined by specific structural organization and the presence of specific chemical substances and ocular pigments. Pathological states result in physical and chemical changes to the tissue. Spectral imaging exploits the differences in the spectral characteristics to separate different classes of material. When these spectral properties are combined with the spatial context of the image, improved visualization and detection is possible. Methods. Two independent spectral imaging devices were developed and integrated to a commercially available Zeiss fundus camera. Spectral data were collected in order to characterize the normal anatomical tissue classes and to assess the usefulness of spectral features for improved class discernment. Spectral images were collected for 14 subjects Diabetic Retinopathy were imaged. Mean spectral curves were produced for each class and for each subject. These spectral curves were normalized to remove the contribution from the pigment melanin (the major pigment associated with variation in fundus pigmentation) and modeled with a piece-wise linear function consisting of a DC offset and four slopes. Results. Differences in the shape of the spectral curve exist between macular edema and normal macular and

  13. Effect of micellar environment on Marcus correlation curves for photoinduced bimolecular electron transfer reactions

    SciTech Connect

    Kumbhakar, Manoj; Nath, Sukhendu; Mukherjee, Tulsi; Pal, Haridas

    2005-07-15

    Photoinduced electron transfer (ET) between coumarin dyes and aromatic amine has been investigated in two cationic micelles, namely, cetyltrimethyl ammonium bromide (CTAB) and dodecyltrimethyl ammonium bromide (DTAB), and the results have been compared with those observed earlier in sodium dodecyl sulphate (SDS) and triton-X-100 (TX-100) micelles for similar donor-acceptor pairs. Due to a reasonably high effective concentration of the amines in the micellar Stern layer, the steady-state fluorescence results show significant static quenching. In the time-resolved (TR) measurements with subnanosecond time resolution, contribution from static quenching is avoided. Correlations of the dynamic quenching constants (k{sub q}{sup TR}), as estimated from the TR measurements, show the typical bell-shaped curves with the free-energy changes ({delta}G{sup 0}) of the ET reactions, as predicted by the Marcus outersphere ET theory. Comparing present results with those obtained earlier for similar coumarin-amine systems in SDS and TX-100 micelles, it is seen that the inversion in the present micelles occurs at an exergonicity (-{delta}G{sup 0}>{approx}1.2-1.3 eV) much higher than that observed in SDS and TX-100 micelles (-{delta}G{sup 0}>{approx}0.7 eV), which has been rationalized based on the relative propensities of the ET and solvation rates in different micelles. In CTAB and DTAB micelles, the k{sub q}{sup TR} values are lower than the solvation rates, which result in the full contribution of the solvent reorganization energy ({lambda}{sub s}) towards the activation barrier for the ET reaction. Contrary to this, in SDS and TX-100 micelles, k{sub q}{sup TR} values are either higher or comparable with the solvation rates, causing only a partial contribution of {lambda}{sub s} in these cases. Thus, Marcus inversion in present cationic micelles is inferred to be the true inversion, whereas that in the anionic SDS and neutral TX-100 micelles are understood to be the apparent

  14. On spectral dependence of polarization of asteroids

    NASA Astrophysics Data System (ADS)

    Lupishko, D. F.; Shkuratov, Yu. G.

    2016-09-01

    From the analysis of all of the data available on the spectral dependence of polarization of light reflected by asteroids, it has been shown that the slope of the spectral dependence of polarization of asteroids changes its sign, when moving from the negative branch of the phase curve of polarization to the positive one. This effect also manifests itself in the spectral behavior of polarization of the Moon and, probably, in the polarization of the other atmosphereless bodies. From the analysis of a population of asteroids of different types, a weak correlation between the spectral slopes of the polarization degree and the albedo has been found.

  15. Ultrafast photoinduced electron transfer in the micelle and the gel phase of a PEO-PPO-PEO triblock copolymer

    SciTech Connect

    Mandal, Ujjwal; Ghosh, Subhadip; Dey, Shantanu; Adhikari, Aniruddha; Bhattacharyya, Kankan

    2008-04-28

    Ultrafast photoinduced electron transfer (PET) from N,N-dimethylaniline (DMA) to coumarin dyes is studied in the micelle and the gel phase of a triblock copolymer, (PEO){sub 20}-(PPO){sub 70}-(PEO){sub 20} (Pluronic P123) by picosecond and femtosecond emission spectroscopies. The rate of PET in a P123 micelle and gel is found to be nonexponential and faster than the slow components of solvation dynamics. In a P123 micelle and gel, PET occurs on multiple time scales ranging from a subpicosecond time scale to a few nanoseconds. In the gel phase, the highest rate constant (9.3x10{sup 9} M{sup -1} s{sup -1}) of ET for C152 is about two times higher than that (3.8x10{sup 9} M{sup -1} s{sup -1}) observed in micelle phase. The ultrafast components of electron transfer (ET) exhibits a bell shaped dependence with the free energy change which is similar to the Marcus inversion. Possible reasons for slower PET in P123 micelle compared to other micelles and relative to P123 gel are discussed.

  16. Multidimensional spectral load balancing

    SciTech Connect

    Hendrickson, B.; Leland, R.

    1993-01-01

    We describe an algorithm for the static load balancing of scientific computations that generalizes and improves upon spectral bisection. Through a novel use of multiple eigenvectors, our new spectral algorithm can divide a computation into 4 or 8 pieces at once. These multidimensional spectral partitioning algorithms generate balanced partitions that have lower communication overhead and are less expensive to compute than those produced by spectral bisection. In addition, they automatically work to minimize message contention on a hypercube or mesh architecture. These spectral partitions are further improved by a multidimensional generalization of the Kernighan-Lin graph partitioning algorithm. Results on several computational grids are given and compared with other popular methods.

  17. Rapid and reversible photoinduced switching of a rotaxane crystal

    NASA Astrophysics Data System (ADS)

    Chen, Kai-Jen; Tsai, Ya-Ching; Suzaki, Yuji; Osakada, Kohtaro; Miura, Atsushi; Horie, Masaki

    2016-11-01

    Crystalline phase transitions caused by external stimuli have been used to detect physical changes in the solid-state properties. This study presents the mechanical switching of crystals of ferrocene-containing rotaxane controlled by focused laser light. The expansion and contraction of the crystals can be driven by turning on and off laser light at 445 nm. The irradiation-induced expansion of the crystal involves elongation along the a, b and c axes at 30 °C, whereas heating of the crystal at 105 °C causes the shortening of c axis. The expansions reversibly occur and have the advantage of a rapid relaxation (reverse) process. Single-crystal X-ray crystallography reveals the detailed structural changes of the molecules, corresponding to a change in the size of the crystals on laser irradiation. This molecular crystal behaviour induced by laser irradiation, is demonstrated for the remote control of objects, namely, microparticle transport and microswitching in an electric circuit.

  18. Photoinduced variable stiffness of spiropyran-based composites

    SciTech Connect

    Samoylova, E.; Ceseracciu, L.; Allione, M.; Diaspro, A.; Barone, A. C.; Athanassiou, A.

    2011-11-14

    A quantitative demonstration of reversible stiffness upon appropriate light stimulus in a spiropyran-polymeric composite is presented. The polymeric films containing 3% wt. of the photochromic spiropyran were irradiated with alternating ultraviolet and visible light and the storage modulus was measured. A reversible change in modulus of about 7% was observed. The modulus change was attributed to an interaction of the polar merocyanine with the polymeric chains and/or to a variation of effective free volume induced by merocyanine aggregates formed in the polymer upon ultraviolet irradiation. The effect is fully reversed when the merocyanine isomers turn back to the spiropyran state after visible irradiation.

  19. Optic nerve head topography and retinal structural changes in eyes with macrodisks: a comparative study with spectral domain optical coherence tomography

    PubMed Central

    Öztürker, Zeynep Kayaarası; Eltutar, Kadir; Karini, Belma; Erkul, Sezin Özdogan; Osmanbaşoğlu, Özen Ayrancı; Sultan, Pınar

    2016-01-01

    Purpose To compare optic nerve head parameters, the thicknesses of the peripapillary retinal nerve fiber layer (pRNFL), the macular retinal nerve fiber layer (mRNFL), the ganglion cell complex (GCC), and the ganglion cell–inner plexiform layer (GCIPL) in macrodisks and normal-sized healthy disks using spectral domain optical coherence tomography. Patients and methods A total of 88 healthy eyes (42 macrodisks and 46 normal-sized disks) were prospectively enrolled in the study. Optic nerve head parameters as well as pRNFL, mRNFL, GCC, and GCIPL thicknesses were measured in all subjects. Optic disk areas (ODAs) >2.70 mm2 were defined as macrodisks. All spectral domain optical coherence tomography parameters were compared between normal-sized disks and macrodisks. Results The mean age of the participants was 49.4±5.7 years in the normal size group and 51.55±6.3 years in the macrodisk group (P=0.65). The average ODAs were 2.23±0.29 mm2 and 3.30±0.59 mm2 in the normal size and the macrodisk groups, respectively. ODA (P<0.001), cup area (P<0.001), cup disk area ratio (P<0.001), horizontal cup disk ratio (P<0.001), vertical cup disk ratio (P<0.001), horizontal disk diameter (P<0.001), vertical disk diameter (P<0.001), and cup volume (P<0.001) were significantly higher in the macrodisk group. The inferior mRNFL thickness was significantly lower (P=0.042), and the GCC inferior and GCIPL inferior thicknesses were found to be lower with low significance (P=0.052, P=0.059, respectively) in the macrodisk group. Rim volume (P=0.622), total pRNFL (P=0.201), superior pRNFL (P=0.123), inferior pRNFL (P=0.168), average macular thickness (P=0.162), total mRNFL (P=0.171), superior mRNFL (P=0.356), total GCC (P=0.080), superior GCC (P=0.261), total GCIPL (P=0.214), and superior GCIPL (P=0.515) thicknesses were similar in both groups. Conclusion Optic disk topography and retinal structures show different characteristics in healthy eyes with macrodisks. These disk size

  20. Experimental and Model Study of Changes in Spectral Solar Irradiance in the Atmosphere of Large City due to Tropospheric NO{sub 2} Content

    SciTech Connect

    Chubarova, N. Ye.; Lebedev, V. V.; Partola, V. S.; Larin, I. K.; Lezina, Ye. A.; Rublev, A. N.

    2009-03-11

    An experimental and model approach has been used to study the NO{sub 2} vertical profiles and its effect on solar irradiance. The profiles of NO{sub 2} were obtained using gas analyzers, which had been installed at different levels at the Moscow State University (MSU) located at the south-western part of Moscow and at the Ostankino tower located at the north of Moscow up to the height of 350 m. Using these data diurnal and spatial variability of the NO{sub 2} content in the most polluted part of planetary boundary layer (PBL) has been analyzed within the large megalopolis. On the base of photochemical modeling we have simulated the diurnal cycle of NO{sub 2} vertical profiles for summer and winter conditions and have compared the results with the experimental ones. Using the RT modeling with input gaseous and aerosol parameters of the atmosphere obtained from the MSU Meteorological Observatory we have estimated the attenuation of spectral solar irradiance in UV and visible region of spectrum due to the NO{sub 2} content in the polluted atmosphere for different seasons.

  1. Surface ligands affect photoinduced modulation of the quantum dots optical performance

    NASA Astrophysics Data System (ADS)

    Krivenkov, Victor A.; Samokhvalov, Pavel S.; Linkov, Pavel A.; Solovyeva, Daria O.; Kotkovskii, Gennadii E.; Chistyakov, Alexander A.; Nabiev, Igor

    2014-05-01

    Changes of optical properties of the solutions of CdSe/ZnS quantum dots (QDs) covered with the trioctylphosphine oxide (TOPO) ligands under the pulsed ultraviolet (UV) laser irradiation are observed. The fluorescence quantum yield (QY) of QDs decreases by more than an order of magnitude when the radiation dose approaches 2 × 10-15 J per particle. This process is accompanied by a blue shift of both fluorescence and the first excitonic absorption peaks. The fluorescence quenching becomes less pronounced when the overall TOPO content in the solution is increased. When ТОРО ligands are replaced with n-hexadecylamine (HDA), QY and spectral properties are not changed at the same irradiation conditions. We assume that the above changes of the optical properties are associated with photooxidation of TOPO ligands by excited QD. Such process is less probable for the HDA ligand due to its different energy structure.

  2. LOVTRAP, An Optogenetic System for Photo-induced Protein Dissociation

    PubMed Central

    Wang, Hui; Vilela, Marco; Winkler, Andreas; Tarnawski, Miroslaw; Schlichting, Ilme; Yumerefendi, Hayretin; Kuhlman, Brian; Liu, Rihe; Danuser, Gaudenz; Hahn, Klaus M

    2016-01-01

    Here we introduce LOVTRAP, an optogenetic approach for reversible, light-induced protein dissociation. LOVTRAP is based on protein A fragments that bind to the LOV domain only in the dark, with tunable kinetics and a >150-fold change in Kd. By reversibly sequestering proteins at mitochondria, we precisely modulated the proteins’ access to the cell edge, demonstrating a naturally occurring 3 mHz cell edge oscillation driven by interactions of Vav2, Rac1 and PI3K. PMID:27427858

  3. Rapid and reversible photoinduced switching of a rotaxane crystal

    PubMed Central

    Chen, Kai-Jen; Tsai, Ya-Ching; Suzaki, Yuji; Osakada, Kohtaro; Miura, Atsushi; Horie, Masaki

    2016-01-01

    Crystalline phase transitions caused by external stimuli have been used to detect physical changes in the solid-state properties. This study presents the mechanical switching of crystals of ferrocene-containing rotaxane controlled by focused laser light. The expansion and contraction of the crystals can be driven by turning on and off laser light at 445 nm. The irradiation-induced expansion of the crystal involves elongation along the a, b and c axes at 30 °C, whereas heating of the crystal at 105 °C causes the shortening of c axis. The expansions reversibly occur and have the advantage of a rapid relaxation (reverse) process. Single-crystal X-ray crystallography reveals the detailed structural changes of the molecules, corresponding to a change in the size of the crystals on laser irradiation. This molecular crystal behaviour induced by laser irradiation, is demonstrated for the remote control of objects, namely, microparticle transport and microswitching in an electric circuit. PMID:27808090

  4. SPATIAL AND SPECTRAL RESOLUTION IN GEOBOTANY.

    USGS Publications Warehouse

    Milton, Nancy M.; Mouat, D.A.

    1984-01-01

    Remotely sensed data are now available from a wide variety of instruments, each data set having a particular spectral and spatial resolution. The changes in vegetation associated with changes in lithology or the presence of mineral deposits can also occur at different scales. The task of geobotanical remote sensing is to choose or adapt the remotely sensed data to the appropriate geobotanical technique to solve the geological problem of interest. Examples are given of a number of applications of data sets of different spectral and spatial resolution. The relative importance of spectral and spatial resolution is discussed.

  5. Sequential Assembly of Magnetic Prussian Blue Films with Photo-Induced Magnetism

    NASA Astrophysics Data System (ADS)

    Meisel, Mark W.

    2004-11-01

    Despite interest in the area of molecule-based magnets, there are few efforts to investigate magnetism in monolayers, surface layers, and other thin films based on these materials. New synthetic methods developed by our groups now permit deposition of single layer and multilayer thin films of cyanometallate molecule-based magnet systems. These monolayers and surface films are inherently anisotropic, thereby allowing magnetic characterizations that are only possible because of our method of fabrication. Two examples will be presented. The distance dependence of dipolar interactions on magnetic order is illustrated by comparing a monolayer, bilayer, and multilayers of a mixed organic/inorganic Fe^3+/Ni^2+ cyanometallate two-dimensional network. The magnetometry results demonstrate the influence of dipolar interactions at an interlayer separation of greater than 35 ÅSecondly, anisotropic response of the photoinduced magnetism in a thin film of Rb_jCo_k[Fe(CN)_6]l \\cdot nH_2O, which experiences a ferrimagnetic transition near 20 K, has been discovered. The photo-induced magnetism may result in a net increase or decrease of the total magnetization of the sample when the externally applied magnetic field is oriented parallel or perpendicular to the plane of the films. The strength of this anisotropy depends on the thickness of the film and the size of the magnetic domains, and the photo-induced magnetism was effective in magnetic fields up to 27 T while at 4.7 K. This work, co-authored with D. R. Talham, was performed with J.-H. Park, F. Frye, Y.-D. Huh, E. Čižmár, and S. Lane, and was supported, in part, by NSF DMR-0305371.

  6. Deuterium enrichment by selective photoinduced dissociation of a multihalogenated organic compound

    DOEpatents

    Marling, John B.; Herman, Irving P.

    1981-01-01

    A method for deuterium enrichment by photoinduced dissociation which uses as the deuterium source a multihalogenated organic compound selected from the group consisting of a dihalomethane, a trihalomethane, a 1,2-dihaloethene, a trihaloethene, a tetrahaloethane and a pentahaloethane. The multihalogenated organic compound is subjected to intense infrared radiation at a preselected wavelength to selectively excite and thereby induce dissociation of substantially only those molecules containing deuterium to provide a deuterium enriched dissociation product. The deuterium enriched product may be combusted with oxygen to provide deuterium enriched water. The deuterium depleted undissociated molecules may be redeuterated by treatment with a deuterium source such as water.

  7. Image storage in coumarin-based copolymer thin films by photoinduced dimerization.

    PubMed

    Gindre, Denis; Iliopoulos, Konstantinos; Krupka, Oksana; Champigny, Emilie; Morille, Yohann; Sallé, Marc

    2013-11-15

    We report a technique to encode grayscale digital images in thin films composed of copolymers containing coumarins. A nonlinear microscopy setup was implemented and two nonlinear optical processes were used to store and read information. A third-order process (two-photon absorption) was used to photoinduce a controlled dimer-to-monomer ratio within a defined tiny volume in the material, which corresponds to each recorded bit of data. Moreover, a second-order process (second-harmonic generation) was used to read the stored information, which has been found to be highly dependent upon the monomer-to-dimer ratio.

  8. Tuning of photoinduced energy transfer in a bichromophoric coumarin supermolecule by cation binding

    SciTech Connect

    Valeur, B.; Pouget, J.; Bourson, J.; Kaschke, M.; Ernsting, N.P.

    1992-08-06

    This paper discussed tuning of photoinduced electronic energy transfer in two coumarins linked by a pentakis (ethylene oxide) spacer by Pb{sup 2+} binding in acetonitrile and propylene carbonate. The ligand:metal ratio is observed to be 1:1 in acetonitrile with a significant increase in efficiency and rate of energy transfer as compared to propylene carbonate, which has a ratio of 1:3. This may be due to a different complex structure in the two solvents. 12 refs., 10 figs., 1 tab.

  9. Graphene/CdTe heterostructure solar cell and its enhancement with photo-induced doping

    SciTech Connect

    Lin, Shisheng Chen, Hongsheng; Li, Xiaoqiang; Zhang, Shengjiao; Wang, Peng; Xu, Zhijuan; Zhong, Huikai; Wu, Zhiqian

    2015-11-09

    We report a type of solar cell based on graphene/CdTe Schottky heterostructure, which can be improved by surface engineering as graphene is atomic thin. By coating a layer of ultrathin CdSe quantum dots onto graphene/CdTe heterostructure, the power conversion efficiency is increased from 2.08% to 3.10%. Photo-induced doping is mainly accounted for this enhancement, as evidenced by field effect transport, Raman, photoluminescence, and quantum efficiency measurements. This work demonstrates a feasible way of improving the performance of graphene/semiconductor heterostructure solar cells by combining one dimensional with two dimensional materials.

  10. Photoinduced charge transfer involving a MoMo quadruply bonded complex to a perylene diimide.

    PubMed

    Alberding, Brian G; Brown-Xu, Samantha E; Chisholm, Malcolm H; Epstein, Arthur J; Gustafson, Terry L; Lewis, Sharlene A; Min, Yong

    2013-04-21

    Evidence, based on femtosecond transient absorption and time resolved infrared spectroscopy, is presented for photoinduced charge transfer from the Mo2δ orbital of the quadruply bonded molecule trans-Mo2(T(i)PB)2(BTh)2, where T(i)PB = 2,4,6-triisopropyl benzoate and BTh = 2,2'-bithienylcarboxylate, to di-n-octyl perylene diimide and di-n-hexylheptyl perylene diimide in thin films and solutions of the mixtures. The films show a long-lived charge separated state while slow back electron transfer, τBET ~ 500 ps, occurs in solution.

  11. Photoinduced Electron Transfer in Ordered Macromolecular Assemblies. Final report for May 1, 1988 - June 30, 2002

    SciTech Connect

    Jones, G.

    2005-02-11

    The final report describes studies over a 13 year period having to do with photoinduced electron transfer for active chromophores and redox agents, including assembly of the components in water soluble polymers or polypeptides. The findings include observation of long range charge separation and electron transport using laser phototransient spectroscopy. The systems targeted in these studies include peptide assemblies for which helical conformations and aggregation are documented. Oligomeric peptides modified with non-native redox active groups were also selected for investigation. Highly charged polymers or peptides were investigated as host agents that resemble proteins. The overall goal of these investigations focused on the design and characterization of systems capable of artificial photosynthesis.

  12. Molecular orbital assistance in the design of intramolecular and photoinduced electron transfer systems

    NASA Astrophysics Data System (ADS)

    Petsalakis, Ioannis D.; Theodorakopoulos, Giannoula

    2012-02-01

    A theoretical approach is described for the design of donor-acceptor intramolecular charge transfer (ICT) systems and for photoinduced electron transfer (PET) hybrids of fullerene, based on orbital level diagrams of the separate donor and acceptor moieties. Minimization of the HOMO-LUMO (highest occupied-lowest unoccupied orbital) gap in ICT systems, translates to a requirement for near degeneracy of the HOMO of the donor and LUMO of the acceptor, determined separately for the two moieties by density functional theory calculations. Similarly, near degeneracy of the LUMO of the donor and LUMO of the acceptor moieties would indicate the possibility of PET in the combined hybrid.

  13. Photoinduced Barkhausen effect in the ferromagnetic semiconductor (Ga,Mn)As.

    PubMed

    Astakhov, G V; Schwittek, J; Schott, G M; Gould, C; Ossau, W; Brunner, K; Molenkamp, L W

    2011-01-21

    Magnetization of ferromagnetic materials commonly occurs via random jumps of domain walls between pinning sites, a phenomenon known as the Barkhausen effect. Using strongly focused light pulses of appropriate power and duration we demonstrate the ability to selectively activate single jumps in the domain wall propagation in (Ga,Mn)As, manifesting itself as a discrete photoinduced domain wall creep as a function of illumination time. The propagation velocity can be increased over 7 orders of magnitude varying the illumination power density and the magnetic field.

  14. Primary ultrafast events preceding the photoinduced proton transfer from pyranine to water

    NASA Astrophysics Data System (ADS)

    Tran-Thi, T.-H.; Gustavsson, T.; Prayer, C.; Pommeret, S.; Hynes, James T.

    2000-10-01

    Femtosecond fluorescence and absorption spectroscopies are used to probe the early events of the photoinduced proton transfer (PT) from pyranine to water. The process is found to involve two ultrafast steps (300 fs and 2.5 ps) which precede the relatively slow (87 ps) PT step. From the comparative study of the properties of the excited acid and its conjugate anion in various aqueous and alcoholic media, these ultrafast steps are identified as the solvation dynamics of the locally excited (LE) state of the acid and its subsequent relaxation to an intermediate electronic state, whose nature is discussed.

  15. Photoinduced Reconfiguration Cycle in a Molecular Adsorbate Layer Studied by Femtosecond Inner-Shell Photoelectron Spectroscopy

    SciTech Connect

    Dachraoui, H.; Michelswirth, M.; Bartz, P.; Pfeiffer, W.; Heinzmann, U.; Siffalovic, P.; Schaefer, C.; Schnatwinkel, B.; Mattay, J.; Drescher, M.

    2011-03-11

    A time-resolved study of core-level chemical shifts in a monolayer of aromatic molecules reveals complex photoinduced reaction dynamics. The combination of electron spectroscopy for chemical analysis and ultrashort pulse excitation in the extreme ultraviolet allows performing time-correlated 4d-core-level spectroscopy of iodine atoms that probe the local chemical environment in the adsorbate molecule. The selectivity of the method unveils metastable molecular configurations that appear about 50 ps after the excitation and are efficiently quenched back to the ground state.

  16. Decay of photoinduced oscillations of the optical reflection coefficient of bismuth

    SciTech Connect

    Semenov, A. L.

    2013-07-15

    A model describing the decay of photoinduced oscillations of the optical reflection coefficient R of bismuth is constructed, taking the crystal lattice anharmonicity into account. The decay time of oscillations of R is calculated as a function of the energy density of a laser pulse. The results of calculations explain the experimental data on the anomalously strong decay of oscillations of the optical reflection coefficient of bismuth (the decay time decreases by more than an order of magnitude with an increase in the laser pulse energy density from 0 to 4 mJ/cm{sup 2})

  17. Fourier transform infrared spectrum of the radical cation of beta-carotene photoinduced in photosystem II.

    PubMed

    Noguchi, T; Mitsuka, T; Inoue, Y

    1994-12-19

    A Fourier-transform infrared (FTIR) spectrum of the radical cation of beta-carotene photoinduced in photosystem II (PSII) membranes was obtained at 80K under oxidizing conditions, by utilizing the light-induced FTIR difference technique. Formation of the beta-carotene cation was monitored with the electronic absorption band at 993 nm. An FTIR spectrum of a chemically-generated beta-carotene cation in chloroform was also measured and compared with the spectrum of PSII. Since the FTIR bands of carotenoid cation have characteristic features with strong intensities, they can be useful markers in studying the reaction of carotenoid in PSII.

  18. Photoinduced electron transfer in rigidly linked dimethoxynapthalene-N-methylpyridinium donor-acceptor molecules

    NASA Astrophysics Data System (ADS)

    Clayton, Andrew H. A.; Ghiggino, Kenneth P.; Wilson, Gerard J.; Keyte, Peter J.; Paddon-Row, Michael N.

    1992-07-01

    Photoinduced electron transfer (ET) is studied in a series of novel molecules containing a dimethoxynaphthalene (DMN) donor and either a pyridine (P) or N-methylpyridinium (P-Me +) acceptor covalently linked via a rigid nonbornalogous bridge ( n sigma bonds in length). ET rates of the order of 10 10 s -1 were measured for the DMN- n-P-Me + series ( n = 4, 6), while no appreciable ET was observed for the DMN- n-P compounds. Electronic and nuclear factors are discussed and the results rationalized in terms of Marcus—Hush and non-adiabatic ET theories.

  19. Linear and Nonlinear Optical Spectroscopy at the Nanoscale with Photoinduced Force Microscopy.

    PubMed

    Jahng, Junghoon; Fishman, Dmitry A; Park, Sung; Nowak, Derek B; Morrison, Will A; Wickramasinghe, H Kumar; Potma, Eric O

    2015-10-20

    The enormous advances made in nanotechnology have also intensified the need for tools that can characterize newly synthesized nanoaterials with high sensitivity and with high spatial resolution. Many existing tools with nanoscopic resolution or better, including scanning electron microscopy (SEM), atomic force microscopy (AFM), and scanning tunneling microscopy (STM) methods, can generate highly detailed maps of nanoscopic structures. However, while these approaches provide great views of the morphological properties of nanomaterials, it has proven more challenging to derive chemical information from the corresponding images. To address this issue, attempts have been made to dress existing nanoscopy methods with spectroscopic sensitivity. A powerful approach in this direction is the combination of scan probe techniques with optical illumination, which aims to marry the nanoscopic resolution provided by a sharp tip with the chemical selectivity provided by optical spectroscopy. Examples of this approach include existing techniques such as scattering-type scanning near-field optical microscopy and tip-enhanced Raman spectroscopy. A new and emerging technique in this direction is photoinduced force microscopy (PiFM), which enables spectroscopic probing of materials with a spatial resolution well under 10 nm. In PiFM, the sample is optically excited and the response of the material is probed directly in the near-field by reading out the time-integrated force between the tip and the sample. Because the magnitude of the force is dependent on the photoinduced polarization in the sample, PiFM exhibits spectroscopic sensitivity. The photoinduced forces measured in PiFM are spatially confined on the nanometer scale, which translates into a very high spatial resolution even under ambient conditions. The PiFM approach is compatible with a wide range optical excitation frequencies, from the visible to the mid-infrared, enabling nanoscale imaging contrast based on either

  20. Time-Resolved Studies of Photoinduced Birefringence in Azobenzene Dye-Doped Polymer Films

    DTIC Science & Technology

    2008-10-01

    state, where the fairly limited work has been done [8,9]. Here we report on transient photoinduced birefrin- gence ( PIB ) measurements on several azo...response time ranges from within 20ns to more than 200 μs. Our results show the response time of PIB to be sys- tematically related to the size of the...lowest optical transition energy. Furthermore, our results suggest that PIB effects can be used to discriminate between0003-6935/08/285074-04$15.00/0

  1. Photoinduced Intramolecular Cyclopentanation vs Photoprotolytic Oxametathesis in Polycyclic Alkenes Outfitted with Conformationally Constrained Aroylmethyl Chromophores‡

    PubMed Central

    Valiulin, Roman A.; Arisco, Teresa M.; Kutateladze, Andrei G.

    2012-01-01

    Intramolecular photoinduced cyclizations are investigated in photoprecursors assembled in a modular fashion via a Diels-Alder reaction of acetylenic dienophiles with subsequent Michael additions of aromatic ketones to install a chromophore capable of initiating Paternò-Büchi cycloadditions or radical cyclization cascades. The protolytic oxametathesis in these systems allows for rapid access to novel polycyclic scaffolds decorated by formyl groups and carboxylates suitable for subsequent modifications. In conformationally constrained photoprecursors a radical rearrangement takes place resulting in intramolecular 1,3-diradical cyclopentanation of the double bond. PMID:23106813

  2. Model of photo-induced neutral-ionic phase transition in organic charge-transfer salts

    NASA Astrophysics Data System (ADS)

    Yartsev, V. M.

    1998-01-01

    One-dimensional donor-acceptor mixed chains are modeled by a periodic DADA tetramer. Electron coupling to intramolecular vibrations are taken into account explicitly. Generalized adiabatic potentials are calculated for the cases of regular and dimerized stacks which are characteristic, respectively, of quasi-neutral (N) and quasi-ionic (I) phases of a tetrathiafulvalene-chloranil compound. A sharp difference in life-times of photo-induced I-states in the N-phase and N-states in the I-phase is discussed within the periodic DADA tetramer model.

  3. Photoinduced cytotoxicity by a platinum diimine complex employing magnetite-silica nanocomposites as delivery vehicles.

    PubMed

    Zhang, Zhigang; Li, Haisha; Dai, Ruihui; Chai, Aiyun

    2015-10-01

    Tartaric acid-modified core-shell magnetite-silica nanocomposites were prepared by a sol-gel method, and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and dynamic light scattering. Then the nanocomposites were employed as carriers of a photoactive platinum diimine complex. Photoinduced cytotoxicity by the photosensitizer-loaded nanocomposites in different human carcinoma cells has been studied by cell viability assay. The results suggest that the as-synthesized nanocomposites have good stability in water, and the cytotoxicity induced by the platinum diimine complex in red light can be significantly enhanced when the photosensitizer is loaded with the magnetic nanocomposites.

  4. Spontaneous photoinduced patterning of azo-dye polymer films: the facts

    SciTech Connect

    Hubert, Christophe

    2007-08-15

    We describe the spontaneous photoinduced patterning of azo-dye polymer films. We have observed that the illumination of an azo-dye polymer film by a uniform single laser beam with normal incidence leads to a self-structurization process that results in the formation of well-ordered submicrometer-sized structures whose organization depends on the light polarization direction. A modulation depth as high as 100 nm can be achieved. The influence of several experimental parameters on the structure formation is studied. Results are discussed and confronted to different models and phenomena already investigated in the literature. A physical origin to this peculiar photopatterning process is proposed.

  5. Deuterium enrichment by selective photo-induced dissociation of an organic carbonyl compound

    DOEpatents

    Marling, John B.

    1981-01-01

    A method for producing a deuterium enriched material by photoinduced dissociation which uses as the working material a gas phase photolytically dissociable organic carbonyl compound containing at least one hydrogen atom bonded to an atom which is adjacent to a carbonyl group and consisting of molecules wherein said hydrogen atom is present as deuterium and molecules wherein said hydrogen atom is present as another isotope of hydrogen. The organic carbonyl compound is subjected to intense infrared radiation at a preselected wavelength to selectively excite and thereby induce dissociation of the deuterium containing species to yield a deuterium enriched stable molecular product. Undissociated carbonyl compound, depleted in deuterium, is preferably redeuterated for reuse.

  6. Photoinduced holographic surface relief gratings in thin self-developing dichromated polymer films: parametric study

    NASA Astrophysics Data System (ADS)

    Beaulieu, Rene M.; Lessard, Roger A.; Bolte, Michel

    1998-09-01

    Photoinduced holographic surface relief gratings have been fabricate din dichromated poly(acrylic acid) films. These gratings are formed in darkness subsequent to the illumination at 442 nm and they are obtained without any chemical treatment or wet processing. The influence of chemical parameters, such as ammonium dichromate and dimethylformamide concentrations, on the holographic characteristics of these gratings have been investigated. Holographic characteristics of the recording medium such as diffraction efficiency as a function of exposure, ammonium dichromate and dimethylformamide concentrations, and spatial frequency are presented in this paper.

  7. POLARON DYNAMICS. Long-lived photoinduced polaron formation in conjugated polyelectrolyte-fullerene assemblies.

    PubMed

    Huber, Rachel C; Ferreira, Amy S; Thompson, Robert; Kilbride, Daniel; Knutson, Nicholas S; Devi, Lekshmi Sudha; Toso, Daniel B; Challa, J Reddy; Zhou, Z Hong; Rubin, Yves; Schwartz, Benjamin J; Tolbert, Sarah H

    2015-06-19

    The efficiency of biological photosynthesis results from the exquisite organization of photoactive elements that promote rapid movement of charge carriers out of a critical recombination range. If synthetic organic photovoltaic materials could mimic this assembly, charge separation and collection could be markedly enhanced. We show that micelle-forming cationic semiconducting polymers can coassemble in water with cationic fullerene derivatives to create photoinduced electron-transfer cascades that lead to exceptionally long-lived polarons. The stability of the polarons depends on the organization of the polymer-fullerene assembly. Properly designed assemblies can produce separated polaronic charges that are stable for days or weeks in aqueous solution.

  8. Photoinduced intramolecular charge transfer process of betaine pyridinium: A theoretical spectroscopic study

    NASA Astrophysics Data System (ADS)

    Perrier, Aurélie; Aloïse, Stéphane; Pawlowska, Zuzanna; Sliwa, Michel; Maurel, François; Abe, Jiro

    2011-10-01

    Using Time-Dependent Density Functional Theory and taking into account bulk solvent effects, we investigate the absorption and emission spectra of a betaine pyridinium molecule, the 2-(1-pyridinio) benzimidazolate (SBPa). This molecule exhibits strong photoinduced intramolecular charge transfer (ICT). We have identified two different electronic states involved, respectively, in the strong bathochromic ICT absorption band (S 2) and in the moderate emission band (S 1). The ICT process is analyzed in terms of charge distribution and dipole moment evolutions upon photoexcitation. These results are compared with steady-state spectroscopic measurements.

  9. Photo-induced conductance fluctuations in mesoscopic Ge/Si systems with quantum dots

    SciTech Connect

    Stepina, N. P.; Dvurechenskii, A. V.; Nikiforov, A. I.; Moers, J.; Gruetzmacher, D.

    2014-08-20

    We study the evolution of electron transport in strongly localized mesoscopic system with quantum dots under small photon flux. Exploring devices with narrow transport channels lead to the observation of giant fluctuations of the photoconductance, which is attributed to the strong dependence of hopping current on the filling of dots by holes. In our experiments, single-photon mode operation is indicated by the linear dependence of the frequency of photo-induced fluctuations on the light intensity and the step-like response of conductance on the pulse excitation. The effect of the light wavelength, measurement temperature, size of the conductive channel on the device efficiency are considered.

  10. Plasmonic electromagnetic hot spots temporally addressed by photoinduced molecular displacement.

    SciTech Connect

    Juan, M. L.; Plain, J.; Bachelot, R.; Vial, A.; Royer, P.; Gray, S. K.; Montgomery, J. M.; Wiederrecht, G. P.; Univ. de Technologie de Troyes

    2009-04-23

    We report the observation of temporally varying electromagnetic hot spots in plasmonic nanostructures. Changes in the field amplitude, position, and spatial features are induced by embedding plasmonic silver nanorods in the photoresponsive azo-polymer. This polymer undergoes cis?trans isomerization and wormlike transport within resonant optical fields, producing a time-varying local dielectric environment that alters the locations where electromagnetic hot spots are produced. Finite-difference time-domain and Monte Carlo simulations that model the induced field and corresponding material response are presented to aid in the interpretation of the experimental results. Evidence for propagating plasmons induced at the ends of the rods is also presented.

  11. Changes in agricultural cropland areas between a water-surplus year and a water-deficit year impacting food security, determined using MODIS 250 m time-series data and spectral matching techniques, in the Krishna river basin (India)

    USGS Publications Warehouse

    Gumma, M.K.; Thenkabail, P.S.; Muralikrishna, I.V.; Velpuri, M.N.; Gangadhararao, P.T.; Dheeravath, V.; Biradar, C.M.; Nalan, S.A.; Gaur, A.

    2011-01-01

    The objective of this study was to investigate the changes in cropland areas as a result of water availability using Moderate Resolution Imaging Spectroradiometer (MODIS) 250 m time-series data and spectral matching techniques (SMTs). The study was conducted in the Krishna River basin in India, a very large river basin with an area of 265 752 km2 (26 575 200 ha), comparing a water-surplus year (2000-2001) and a water-deficit year (2002-2003). The MODIS 250 m time-series data and SMTs were found ideal for agricultural cropland change detection over large areas and provided fuzzy classification accuracies of 61-100% for various land-use classes and 61-81% for the rain-fed and irrigated classes. The most mixing change occurred between rain-fed cropland areas and informally irrigated (e.g. groundwater and small reservoir) areas. Hence separation of these two classes was the most difficult. The MODIS 250 m-derived irrigated cropland areas for the districts were highly correlated with the Indian Bureau of Statistics data, with R2-values between 0.82 and 0.86. The change in the net area irrigated was modest, with an irrigated area of 8 669 881 ha during the water-surplus year, as compared with 7 718 900 ha during the water-deficit year. However, this is quite misleading as most of the major changes occurred in cropping intensity, such as changing from higher intensity to lower intensity (e.g. from double crop to single crop). The changes in cropping intensity of the agricultural cropland areas that took place in the water-deficit year (2002-2003) when compared with the water-surplus year (2000-2001) in the Krishna basin were: (a) 1 078 564 ha changed from double crop to single crop, (b) 1 461 177 ha changed from continuous crop to single crop, (c) 704 172 ha changed from irrigated single crop to fallow and (d) 1 314 522 ha changed from minor irrigation (e.g. tanks, small reservoirs) to rain-fed. These are highly significant changes that will have strong impact on food

  12. Evaluating Spectral Signals to Identify Spectral Error

    PubMed Central

    Bazar, George; Kovacs, Zoltan; Tsenkova, Roumiana

    2016-01-01

    Since the precision and accuracy level of a chemometric model is highly influenced by the quality of the raw spectral data, it is very important to evaluate the recorded spectra and describe the erroneous regions before qualitative and quantitative analyses or detailed band assignment. This paper provides a collection of basic spectral analytical procedures and demonstrates their applicability in detecting errors of near infrared data. Evaluation methods based on standard deviation, coefficient of variation, mean centering and smoothing techniques are presented. Applications of derivatives with various gap sizes, even below the bandpass of the spectrometer, are shown to evaluate the level of spectral errors and find their origin. The possibility for prudent measurement of the third overtone region of water is also highlighted by evaluation of a complex data recorded with various spectrometers. PMID:26731541

  13. Raman Investigation of Structural Photoinduced Irreversible Changes of Ga(10)Ge(25)S(65) Chalcogenide Glasses

    DTIC Science & Technology

    2001-06-01

    Inorganic Materials IIC ASCR and ICT, Pelleova 24, Prague 6, Czech Republic blnstituto de Quimica - UNESP- C.P. 355, CEP: 14801-970, Araraquara, SP...Brazil cDepto de Quimica - Universidade Federal de Juiz de Fora, Juiz de Fora, MG- Brazil dEscola de Engenharia de Sao Carlos- - Universidade de Sao Paulo

  14. Preparation of TiO2 thin films using water-soluble titanium complexes and their photoinduced properties.

    PubMed

    Katsumata, Ken-ichi; Ohno, Yukiaki; Tomita, Koji; Sakai, Munetoshi; Nakajima, Akira; Kakihana, Masato; Fujishima, Akira; Matsushita, Nobuhiro; Okada, Kiyoshi

    2011-01-01

    Titanium dioxide thin films were prepared by using four water-soluble titanium complexes of titanium-lactate, tartalate, malate and salicylate complex solutions. The crystalline phases detected in the films were anatase. The surface microstructures of the four film samples were different in their grain sizes. Photocatalytic decomposition activity of the four films was almost the same, but their photoinduced hydrophilicities were different. The film prepared using titanium-salicylate complex exhibited lower hydrophilic conversion rate than the other films. Grain size and stress yielded to the film are considered to be important factors on the photoinduced hydrophilicity.

  15. Engaging Copper(III) Corrole as an Electron Acceptor: Photoinduced Charge Separation in Zinc Porphyrin-Copper Corrole Donor-Acceptor Conjugates.

    PubMed

    Ngo, Thien H; Zieba, David; Webre, Whitney A; Lim, Gary N; Karr, Paul A; Kord, Scheghajegh; Jin, Shangbin; Ariga, Katsuhiko; Galli, Marzia; Goldup, Steve; Hill, Jonathan P; D'Souza, Francis

    2016-01-22

    An electron-deficient copper(III) corrole was utilized for the construction of donor-acceptor conjugates with zinc(II) porphyrin (ZnP) as a singlet excited state electron donor, and the occurrence of photoinduced charge separation was demonstrated by using transient pump-probe spectroscopic techniques. In these conjugates, the number of copper corrole units was varied from 1 to 2 or 4 units while maintaining a single ZnP entity to observe the effect of corrole multiplicity in facilitating the charge-separation process. The conjugates and control compounds were electrochemically and spectroelectrochemically characterized. Computational studies revealed ground state geometries of the compounds and the electron-deficient nature of the copper(III) corrole. An energy level diagram was established to predict the photochemical events by using optical, emission, electrochemical, and computational data. The occurrence of charge separation from singlet excited zinc porphyrin and charge recombination to yield directly the ground state species were evident from the diagram. Femtosecond transient absorption spectroscopy studies provided spectral evidence of charge separation in the form of the zinc porphyrin radical cation and copper(II) corrole species as products. Rates of charge separation in the conjugates were found to be of the order of 10(10)  s(-1) and increased with increasing multiplicity of copper(III) corrole entities. The present study demonstrates the importance of copper(III) corrole as an electron acceptor in building model photosynthetic systems.

  16. ESIPT and photodissociation of 3-hydroxychromone in solution: photoinduced processes studied by static and time-resolved UV/Vis, fluorescence, and IR spectroscopy.

    PubMed

    Chevalier, Katharina; Grün, Anneken; Stamm, Anke; Schmitt, Yvonne; Gerhards, Markus; Diller, Rolf

    2013-11-07

    The spectral properties of fluorescence sensors such as 3-hydroxychromone (3-HC) and its derivatives are sensitive to interaction with the surrounding medium as well as to substitution. 3-HC is a prototype system for other derivatives because it is the basic unit of all flavonoides undergoing ESIPT and is not perturbed by a substituent. In this study, the elementary processes and intermediate states in the photocycle of 3-HC as well as its anion were identified and characterized by the use of static and femtosecond time-resolved spectroscopy in different solvents (methylcyclohexane, acetonitrile, ethanol, and water at different pH). Electronic absorption and fluorescence spectra and lifetimes of the intermediate states were obtained for the normal, tautomer and anionic excited state, while mid-IR vibrational spectra yielded structural information on ground and excited states of 3-HC. A high sensitivity on hydrogen-bonding perturbations was observed, leading to photoinduced anion formation in water, while in organic solvents, different processes are suggested, including slow picosecond ESIPT and contribution of the trans-structure excited state or a different stable solvation state with different direction of OH. The formation of the latter could be favored by the lack of a substituent increasing contact points for specific solute-solvent interactions at the hydroxyl group compared to substituted derivatives. The effect of substituents has to be considered for the design of future fluorescence sensors based on 3-HC.

  17. Spectrally resolved intraband transitions on two-step photon absorption in InGaAs/GaAs quantum dot solar cell

    SciTech Connect

    Tamaki, Ryo Shoji, Yasushi; Okada, Yoshitaka; Miyano, Kenjiro

    2014-08-18

    Two-step photon absorption processes in a self-organized In{sub 0.4}Ga{sub 0.6}As/GaAs quantum dot (QD) solar cell have been investigated by monitoring the mid-infrared (IR) photoinduced modulation of the external quantum efficiency (ΔEQE) at low temperature. The first step interband and the second step intraband transitions were both spectrally resolved by scanning photon energies of visible to near-IR CW light and mid-IR pulse lasers, respectively. A peak centered at 0.20 eV corresponding to the transition to virtual bound states and a band above 0.42 eV probably due to photoexcitation to GaAs continuum states were observed in ΔEQE spectra, when the interband transition was above 1.4 eV, directly exciting wetting layers or GaAs spacer layers. On the other hand, resonant excitation of the ground state of QDs at 1.35 eV resulted in a reduction of EQE. The sign of ΔEQE below 1.40 eV changed from negative to positive by increasing the excitation intensity of the interband transition. We ascribe this to the filling of higher energy trap states.

  18. Spectrally resolved intraband transitions on two-step photon absorption in InGaAs/GaAs quantum dot solar cell

    NASA Astrophysics Data System (ADS)

    Tamaki, Ryo; Shoji, Yasushi; Okada, Yoshitaka; Miyano, Kenjiro

    2014-08-01

    Two-step photon absorption processes in a self-organized In0.4Ga0.6As/GaAs quantum dot (QD) solar cell have been investigated by monitoring the mid-infrared (IR) photoinduced modulation of the external quantum efficiency (ΔEQE) at low temperature. The first step interband and the second step intraband transitions were both spectrally resolved by scanning photon energies of visible to near-IR CW light and mid-IR pulse lasers, respectively. A peak centered at 0.20 eV corresponding to the transition to virtual bound states and a band above 0.42 eV probably due to photoexcitation to GaAs continuum states were observed in ΔEQE spectra, when the interband transition was above 1.4 eV, directly exciting wetting layers or GaAs spacer layers. On the other hand, resonant excitation of the ground state of QDs at 1.35 eV resulted in a reduction of EQE. The sign of ΔEQE below 1.40 eV changed from negative to positive by increasing the excitation intensity of the interband transition. We ascribe this to the filling of higher energy trap states.

  19. Photoinduced electron transfer between Fe(III) and adenosine triphosphate-BODIPY conjugates: Application to alkaline-phosphatase-linked immunoassay.

    PubMed

    Lin, Jia-Hui; Yang, Ya-Chun; Shih, Ya-Chen; Hung, Szu-Ying; Lu, Chi-Yu; Tseng, Wei-Lung

    2016-03-15

    Fluorescent boron dipyrromethene (BODIPY) analogs are often used as sensors for detecting various species because of their relatively high extinction coefficients, outstanding fluorescence quantum yields, photostability, and pH-independent fluorescence. However, there is little-to-no information in the literature that describes the use of BODIPY analogs for detecting alkaline phosphatase (ALP) activity and inhibition. This study discovered that the fluorescence of BODIPY-conjugated adenosine triphosphate (BODIPY-ATP) was quenched by Fe(III) ions through photoinduced electron transfer. The ALP-catalyzed hydrolysis of BODIPY-ATP resulted in the formation of BODIPY-adenosine and phosphate ions. The fluorescence of the generated BODIPY-adenosine was insensitive to the change in the concentration of Fe(III) ions. Thus, the Fe(III)-induced fluorescence quenching of BODIPY-ATP can be paired with its ALP-mediated dephosphorylation to design a turn-on fluorescence probe for ALP sensing. A method detection limit at a signal-to-noise ratio of 3 for ALP was estimated to be 0.02 units/L (~6 pM; 1 ng/mL). This probe was used for the screening of ALP inhibitors, including Na3VO4, imidazole, and arginine. Because ALP is widely used in enzyme-linked immunosorbent assays, the probe was coupled to an ALP-linked immunosorbent assay for the sensitive and selective detection of immunoglobulin G (IgG). The lowest detectable concentration for IgG in this system was 5 ng/mL. Compared with the use of 3,6-fluorescein diphosphate as a signal reporter in an ALP-linked immunosorbent assay, the proposed system provided comparable sensitivity, large linear range, and high stability over temperature and pH changes.

  20. Spectral characterization of the binding and conformational changes of bovine serum albumin upon interaction with an anti-fungal drug, methylparaben

    NASA Astrophysics Data System (ADS)

    Naik, Keerti M.; Nandibewoor, Sharanappa T.

    2013-03-01

    The binding of methylparaben with bovine serum albumin (BSA) was investigated by spectroscopic methods viz., fluorescence, FT-IR and UV-vis absorption techniques under physiological conditions i.e., pH 7.4. Spectroscopic analysis of the emission quenching at different temperatures revealed that the quenching mechanism of bovine serum albumin by methylparaben shows a dynamic quenching. The binding sites number n and binding constants, K were obtained at various temperatures. The distance, r between methylparaben and BSA was evaluated according to the theory of Förster energy transfer. The result of FT-IR spectra and UV-vis absorption spectra showed that the conformation of bovine serum albumin has been changed in the presence of methylparaben. The thermodynamic parameters, enthalpy change (ΔH0) and entropy change (ΔS0) were calculated according to van't Hoff equation, which indicated that the hydrophobic interaction was the predominant intermolecular force stabilizing the complex. The effect of common ions and site probes were also carried on the binding of methylparaben to BSA.

  1. Spectral and Color Changes of Ag/TiO2 Photochromic Films Deposited on Diffusing Paper and Transparent Flexible Plastic Substrates.

    PubMed

    Diop, Daouda K; Simonot, Lionel; Martínez-García, Juan; Hébert, Mathieu; Lefkir, Yaya; Abadias, Grégory; Guérin, Philippe; Babonneau, David; Destouches, Nathalie

    2016-12-12

    Giving paper and polymer photochromic properties under laser irradiation is challenging due to the low resistance of these materials to heat, their flexibility, and their possibly irregular structure. However, we could successfully deposit TiO2/Ag/TiO2 layers stacking on flexible white glossy paper and transparent polyethylene terephalate (PET) substrates using a reactive magnetron sputtering technique, and tailor coloration changes after laser irradiation, alternating visible and ultraviolet (UV) wavelengths. The sample colors are characterized by a panel of chromas depending on the irradiation conditions. We demonstrate that these chroma changes are due to morphological changes of Ag nanoparticles (NPs) after visible laser irradiation of the colored as-deposited sample. The process exhibits a good reversibility after subsequent UV irradiation due to the growth of new metallic Ag NPs. The colors displayed in diffuse reflection by the paper samples are more saturated than the ones displayed in regular transmission by PET samples. We demonstrate the efficiency of the photochromic process on such support by printing high resolution patterns exhibiting different colors depending on the observation conditions.

  2. Parallelism of amino acid changes at the RH1 affecting spectral sensitivity among deep-water cichlids from Lakes Tanganyika and Malawi.

    PubMed

    Sugawara, Tohru; Terai, Yohey; Imai, Hiroo; Turner, George F; Koblmüller, Stephan; Sturmbauer, Christian; Shichida, Yoshinori; Okada, Norihiro

    2005-04-12

    Many examples of the appearance of similar traits in different lineages are known during the evolution of organisms. However, the underlying genetic mechanisms have been elucidated in very few cases. Here, we provide a clear example of evolutionary parallelism, involving changes in the same genetic pathway, providing functional adaptation of RH1 pigments to deep-water habitats during the adaptive radiation of East African cichlid fishes. We determined the RH1 sequences from 233 individual cichlids. The reconstruction of cichlid RH1 pigments with 11-cis-retinal from 28 sequences showed that the absorption spectra of the pigments of nine species were shifted toward blue, tuned by two particular amino acid replacements. These blue-shifted RH1 pigments might have evolved as adaptations to the deep-water photic environment. Phylogenetic evidence indicates that one of the replacements, A292S, has evolved several times independently, inducing similar functional change. The parallel evolution of the same mutation at the same amino acid position suggests that the number of genetic changes underlying the appearance of similar traits in cichlid diversification may be fewer than previously expected.

  3. Changes in the spectral composition of animal-brain electrical activity under the influence of nonthermal millimeter-wave radiation on acupuncture points

    NASA Astrophysics Data System (ADS)

    Khramov, R. N.; Vorob'ev, V. V.

    1994-01-01

    The frequency spectra (0 26 Hz) of electrograms (EG) of the preoptic region of the hypothalamus were studied in chronic experiments on nine awake rabbits under the influence of nonthermal millimeter-band (55 75 GHz) electromagnetic fields on various acupuncture points: I) the auricular “heart” point (after F. G. Portnov); II) the cranial acupoint (TR-20; the “hypothalamus” point after R. Voll); and III) the “longevity” acupoint (E-36). Irradiation of point I was accompanied by significant suppression of hypothalamic electrical activity at 5 and 16 Hz and enhancement at 7 8, 12, and 26 Hz. Irradiation of point II had similar but less-prominent effects at 7 8 and 12 Hz. Minimal EG changes were observed with exposure of point III. The probabilities of significant changes in EG spectra for irradiation of points I, II, and III were, respectively, 31%, 21%, and 5% (p<0.05, U-criterion). These results suggest that acupuncture points I and II are more sensitive to millimeter-band radiation than is point III. The presence of individual characteristics of the effects and their change after stress to sign inversion were shown in rat experiments in which the acupuncture points were irradiated.

  4. The spectral changes in EMG during a second bout eccentric contraction could be due to adaptation in muscle fibres themselves: a simulation study.

    PubMed

    Dimitrov, V G; Arabadzhiev, T I; Dimitrova, N A; Dimitrov, G V

    2012-04-01

    The mechanism of marked reduction in damage symptoms after repeated bout of similar eccentric contractions is still unknown. The neuronal adaptation leading to reduction of muscle fibre propagation velocity (MFPV) due to increased activation of slow-twitch motor units (MUs), decrease in activation of fast-twitch MUs, and/or increase in MU synchronization was suggested as a cause for lower EMG frequency characteristics. However, the repeated bout effect could occur also after electrically stimulated exercise. Prolonged elevation of cytoplasmic Ca(2+) due to the increased membrane permeability after eccentric contractions was reported. Elevated Ca(2+) induced peripheral changes that included alteration of intracellular action potential and MFPV reduction. We simulated and compared changes in EMG frequency characteristics related to effects of central nervous system (CNS) or to peripheral changes. The simulations were performed for different electrode arrangements and positions. The results showed that the peripheral effects could be similar or even stronger than the effects related to CNS. We hypothesised that the repeated bout effect was a consequence of the adaptation in muscle fibres necessary for avoiding Ca(2+)-induced protein and lipid degradation due to Ca(2+) overload resulting from the increased membrane permeability after eccentric contraction. The possibilities for noninvasive testing of this hypothesis were discussed.

  5. Ultrafast photoinduced charge separation in metal-semiconductor nanohybrids.

    PubMed

    Mongin, Denis; Shaviv, Ehud; Maioli, Paolo; Crut, Aurélien; Banin, Uri; Del Fatti, Natalia; Vallée, Fabrice

    2012-08-28

    Hybrid nano-objects formed by two or more disparate materials are among the most promising and versatile nanosystems. A key parameter in their properties is interaction between their components. In this context we have investigated ultrafast charge separation in semiconductor-metal nanohybrids using a model system of gold-tipped CdS nanorods in a matchstick architecture. Experiments are performed using an optical time-resolved pump-probe technique, exciting either the semiconductor or the metal component of the particles, and probing the light-induced change of their optical response. Electron-hole pairs photoexcited in the semiconductor part of the nanohybrids are shown to undergo rapid charge separation with the electron transferred to the metal part on a sub-20 fs time scale. This ultrafast gold charging leads to a transient red-shift and broadening of the metal surface plasmon resonance, in agreement with results for free clusters but in contrast to observation for static charging of gold nanoparticles in liquid environments. Quantitative comparison with a theoretical model is in excellent agreement with the experimental results, confirming photoexcitation of one electron-hole pair per nanohybrid followed by ultrafast charge separation. The results also point to the utilization of such metal-semiconductor nanohybrids in light-harvesting applications and in photocatalysis.

  6. Photoinduced conformational switch of enantiopure azobenzenes controlled by a sulfoxide.

    PubMed

    Carreño, M Carmen; García, Isabel; Núñez, Irene; Merino, Estíbaliz; Ribagorda, María; Pieraccini, Silvia; Spada, Gian Piero

    2007-06-06

    Two series of enantiopure azobenzenes with a p-tolylsulfoxide at the ortho or meta position with respect to the azo group, have been regioselectively synthesized. Both can act as enantiopure molecular switches showing different structural features owing to the presence of the stereogenic sulfur. The photoisomerization process, studied by UV-vis, circular dichroism (CD), NMR, and chiral HPLC evidenced a double role of the sulfoxide. A transfer of chirality from the sulfoxide to the azo system was observed by CD in both cis and trans-isomers of the meta sulfinyl derivatives 3, whereas this perturbation was evident for the ortho sulfinyl series 7 only in the cis isomer. The NMR study evidenced that the s-cis rigid conformation of the bisaromatic sulfoxide was fixing a different orientation of the overall system in each series both in the trans and cis isomers, by forcing a final U-shaped structure in cis-3 and an S-shaped structure in cis-7. Very different values of specific optical rotations were measured in both trans and cis isomers, also reflecting the existence of distinct chiral entities in the photostationary states. The easy and reversible changes occurring between different conformational states could find applications in the photocontrol of several molecular switches.

  7. Photoinduced Oxidation of Arsenite to Arsenate on Ferrihydrite

    SciTech Connect

    N Bhandari; R Reeder; D Strongin

    2011-12-31

    The photochemistry of an aqueous suspension of the iron oxyhydroxide, ferrihydrite, in the presence of arsenite has been investigated using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray absorption near edge structure (XANES), and solution phase analysis. Both ATR-FTIR and XANES show that the exposure of ferrihydrite to arsenite in the dark leads to no change in the As oxidation state, but the exposure of this arsenite-bearing surface, which is in contact with pH 5 water, to light leads to the conversion of the majority of the adsorbed arsenite to the As(V) bearing species, arsenate. Analysis of the solution phase shows that ferrous iron is released into solution during the oxidation of arsenite. The photochemical reaction, however, shows the characteristics of a self-terminating reaction in that there is a significant suppression of this redox chemistry before 10% of the total iron making up the ferrihydrite partitions into solution as ferrous iron. The self-terminating behavior exhibited by this photochemical arsenite/ferrihydrite system is likely due to the passivation of the ferrihydrite surface by the strongly bound arsenate product.

  8. Spectral ratio method for measuring emissivity

    USGS Publications Warehouse

    Watson, K.

    1992-01-01

    The spectral ratio method is based on the concept that although the spectral radiances are very sensitive to small changes in temperature the ratios are not. Only an approximate estimate of temperature is required thus, for example, we can determine the emissivity ratio to an accuracy of 1% with a temperature estimate that is only accurate to 12.5 K. Selecting the maximum value of the channel brightness temperatures is an unbiased estimate. Laboratory and field spectral data are easily converted into spectral ratio plots. The ratio method is limited by system signal:noise and spectral band-width. The images can appear quite noisy because ratios enhance high frequencies and may require spatial filtering. Atmospheric effects tend to rescale the ratios and require using an atmospheric model or a calibration site. ?? 1992.

  9. Photoinduced Enhancement of Anisotropic Charge Correlations on Triangular Lattices with Trimers

    NASA Astrophysics Data System (ADS)

    Yonemitsu, Kenji

    2017-02-01

    To explore nontrivial photoinduced modulations of charge correlations, we theoretically study photoinduced dynamics in quarter-filled extended Hubbard models with competing intersite repulsive interactions on triangular lattices with trimers, where the end points are crystallographically equivalent. The exact diagonalization method is used and the time-dependent Schrödinger equation is numerically solved during and after photoexcitation. Time-averaged double occupancy and intersite density-density correlations can be interpreted as due to effective on-site and intersite repulsive interactions, respectively, relative to transfer energies. In the case where the intersite repulsive interactions compete with each other, the anisotropy of their effective interactions can be enhanced with the help of the trimers, irrespective of whether the trimers are linear or bent. In particular, in the case where the arrangement of the trimers is close to that in α-(bis[ethylenedithio]-tetrathiafulvalene)2I3 [α-(BEDT-TTF)2I3] in the metallic phase, the effective on-site repulsion is enhanced relative to the transfer energies. The relevance of this theoretical finding to the experimentally observed optical freezing of charge motion is discussed.

  10. Tailored heterojunctions for efficient thin-film organic solar cells: a photoinduced absorption study

    NASA Astrophysics Data System (ADS)

    Schueppel, R.; Schmidt, K.; Uhrich, C.; Schulze, K.; Wynands, D.; Brédas, J. L.; Maennig, B.; Pfeiffer, M.; Leo, K.; Brier, E.; Reinold, E.; Bu, H.-B.; Baeuerle, P.

    2007-09-01

    Recently, we have demonstrated an open circuit voltage of 1.0V and a power conversion efficiency of 3.4% in thin film solar cells, utilizing a new acceptor-substituted oligothiophene with an optical gap of 1.77 eV as donor and C 60 as acceptor. Stimulated by this result, we systematically study the energy and electron transfer processes taking place at the oligothiophene:fullerene heterojunction along a homologous series of these oligothiophenes. The heterojunction is modified by tuning the HOMO level using different oligothiophene chain lengths, while the LUMO level is essentially fixed by the choice of the acceptor-type end-groups (dicyanovinyl) attached to the oligothiophene. We study electron transfer at the heterojunction to C 60 using photoinduced absorption. The observed transitions are unambiguously identified by TD-DFT calculations. With increasing the effective energy gap of the donor-acceptor pair, charge carrier dissociation following the photoinduced electron transfer is eventually replaced by recombination into the triplet state, which alters the photovoltaic operation conditions. Therefore, the optimum open-circuit voltage of a solar cell is a trade-off between an efficient charge separation at the interface and a maximized effective gap. We conclude that values between 1.0 and 1.1 V for the open-circuit voltage in our solar cell devices present an optimum, as higher voltages were only achieved with concomitant losses in charge separation efficiency.

  11. Effect of natural organic matter on the photo-induced toxicity of titanium dioxide nanoparticles.

    PubMed

    Wormington, Alexis M; Coral, Jason; Alloy, Matthew M; Damarè, Carmen L; Mansfield, Charles M; Klaine, Stephen J; Bisesi, Joseph H; Roberts, Aaron P

    2016-12-07

    Nano-titanium dioxide (TiO2 ) is the most widely used form of nanoparticles in commercial industry and comes in 2 main configurations: rutile and anatase. Rutile TiO2 is used in ultraviolet (UV) screening applications, whereas anatase TiO2 crystals have a surface defect that makes them photoreactive. There are numerous reports in the literature of photo-induced toxicity to aquatic organisms following coexposure to anatase nano-TiO2 and UV. All natural freshwater contains varying amounts of natural organic matter (NOM), which can drive UV attenuation and quench reactive oxygen species (ROS) in aquatic ecosystems. The present research examined how NOM alters the photo-induced toxicity of anatase nano-TiO2 . Daphnia magna neonates were coexposed to NOM and photoexcited anatase nano-TiO2 for 48 h. Natural organic matter concentrations as low as 4 mg/L reduced anatase nano-TiO2 toxicity by nearly 100%. These concentrations of NOM attenuated UV by <10% in the exposure system. However, ROS production measured using a fluorescence assay was significantly reduced in a NOM concentration--dependent manner. Taken together, these data suggest that NOM reduces anatase nano-TiO2 toxicity via an ROS quenching mechanism and not by attenuation of UV. Environ Toxicol Chem 2016;9999:1-6. © 2016 SETAC.

  12. OPTICAL FIBRES: Photoinduced and thermal reactions involving hydrogen in high-germania-core optical fibres

    NASA Astrophysics Data System (ADS)

    Rybaltovskii, A. O.; Koltashev, V. V.; Medvedkov, O. I.; Rybaltovsky, A. A.; Sokolov, V. O.; Klyamkin, Semen N.; Plotnichenko, V. G.; Dianov, Evgenii M.

    2008-12-01

    We report a Raman scattering study of photoinduced and thermal reactions between H2 and germanosilicate optical fibres with 22 mol % and 97 mol % GeO2 in the core (F1 and F2, respectively) after H2 loading at 150 MPa (1500 atm). The mechanisms of photoreactions are investigated in a wide range of incident laser wavelengths (244, 333, 354, 361 and 514 nm). Thermal reactions are studied at 500 °C. The results indicate that the main mechanism behind the formation of hydrogen-containing defects with Raman bands at 700, 750, 2190, 3600 and 3680 cm-1 involves ≡Ge—O—Ge≡ or ≡Ge—O—Si≡ bond breaking and formation of hydride and hydroxyl species: =GeH2 (700, 750 cm-1), ≡Ge—H (2190 cm-1), ≡GeO—H (3600 cm-1) and ≡SiO—H (3680 cm-1). The key features of the reactions in the F1 and F2 fibres are analysed. In particular, photoinduced reactions give ≡Si—OH groups only in the F1 fibres, whereas the formation of germanium nanoclusters at a relatively low temperature (~500 °C) or ≡GeO—H and ≡Ge—H defects under 514-nm irradiation has only been observed in the F2 fibres.

  13. Effects of photoinduced toxicity of fluoranthene on amphibian embryos and larvae

    SciTech Connect

    Hatch, A.C.; Burton, G.A. Jr.

    1998-09-01

    Embryos and newly hatched larvae of three amphibian species, the spotted salamander (Ambystoma maculatum), the northern leopard frog (Rana pipiens), and the African clawed frog (Xenopus laevis), were exposed to fluoranthene and ultraviolet (UV) light in two scenarios. Embryos were exposed in a laboratory setting from an early developmental stage through hatching under artificial UV light, and newly hatched larvae were exposed outdoors in varying sunlight intensity levels. Outdoor exposures indicated greater sensitivity in the toxic response than did laboratory exposures. In the laboratory, mortality and malformation of X. laevis were the most sensitive indicators of exposure. Xenopus laevis was also the most sensitive species tested to the effects of UV light alone. Hatching success of R. pipiens was monitored outdoors and was not a useful predictive endpoint in the determination of photoinduced toxicity; however, newly hatched larvae were sensitive to the effects of photoinduced toxicity. Amybstoma maculatum and X. laevis larvae were affected by low ({micro}g/L) concentrations of fluoranthene in sunlight. These findings suggest that low levels of polycyclic aromatic hydrocarbons could be acting synergistically with environmental factors such as UV light to place young amphibians at risk.

  14. Tracking of the molecular motion in the primary event of photoinduced reactions of a phytochromobilin model.

    PubMed

    Zhuang, Xuhui; Wang, Jun; Lan, Zhenggang

    2013-12-19

    The photoinduced processes of phytochromes have received great research interest for their important biological functions. Phytochromobilin (PΦB), one of the most important phytochrome chromophores, was selected as the prototype to study its photoinduced isomerization. The nonadiabatic dynamics of PΦB from the Pr configuration in the gas phase was investigated by the surface hopping method at the OM2/MRCI level. In the excited state, isolated PΦB does not display the rotation of the two terminal five-membered rings (ring A and ring D), which is assumed to govern the Pr → Pfr process in the protein. Instead, two S1/S0 conical intersection seams (CI01α and CI01β) characterized by the rotation of the two central rings (ring B and ring C) were proven to play essential roles for the photoisomerization of PΦB in the gas phase. These two conical intersections (CI01α and CI01β) are accessible by the twisting motions of the C9-C10 and C10-C11 bonds, respectively. The CI01α and CI01β seams, instead of their minimum-energy points, are responsible for the nonadiabatic dynamics. For both channels, the trajectories may propagate forward to the isomerization products or backward to the original Pr configuration after the S1 → S0 hops.

  15. Kinetics of photoinduced ordering in azo-dye films: two-state and diffusion models.

    PubMed

    Kiselev, Alexei D; Chigrinov, Vladimir G; Kwok, Hoi-Sing

    2009-07-01

    We theoretically study the kinetics of photoinduced ordering in azo-dye photoaligning layers and present the results of modeling performed using two different phenomenological approaches. A phenomenological two-state model is deduced from the master equation for the one-particle distribution functions of an ensemble of two-level molecular systems by specifying the angular redistribution probabilities and by expressing the order parameter correlation functions in terms of the order parameter tensor. Using an alternative approach that describes light-induced reorientation of azo-dye molecules in terms of a rotational Brownian motion, we formulate the two-dimensional diffusion model as the free energy Fokker-Planck equation simplified for the limiting regime of purely in-plane reorientation. The models are employed to interpret the irradiation time dependence of the absorption order parameters defined in terms of the principal extinction (absorption) coefficients. Using the exact solution to the light transmission problem for a biaxially anisotropic absorbing layer, these coefficients are extracted from the absorbance-vs-incidence angle curves measured at different irradiation doses for the probe light linearly polarized parallel and perpendicular to the plane of incidence. It is found that, in the azo-dye films, the transient photoinduced structures are biaxially anisotropic whereas the photosteady and the initial states are uniaxial.

  16. Kinetics of photoinduced ordering in azo-dye films: Two-state and diffusion models

    SciTech Connect

    Kiselev, Alexei D.; Chigrinov, Vladimir G.; Kwok, Hoi-Sing

    2009-07-15

    We theoretically study the kinetics of photoinduced ordering in azo-dye photoaligning layers and present the results of modeling performed using two different phenomenological approaches. A phenomenological two-state model is deduced from the master equation for the one-particle distribution functions of an ensemble of two-level molecular systems by specifying the angular redistribution probabilities and by expressing the order parameter correlation functions in terms of the order parameter tensor. Using an alternative approach that describes light-induced reorientation of azo-dye molecules in terms of a rotational Brownian motion, we formulate the two-dimensional diffusion model as the free energy Fokker-Planck equation simplified for the limiting regime of purely in-plane reorientation. The models are employed to interpret the irradiation time dependence of the absorption order parameters defined in terms of the principal extinction (absorption) coefficients. Using the exact solution to the light transmission problem for a biaxially anisotropic absorbing layer, these coefficients are extracted from the absorbance-vs-incidence angle curves measured at different irradiation doses for the probe light linearly polarized parallel and perpendicular to the plane of incidence. It is found that, in the azo-dye films, the transient photoinduced structures are biaxially anisotropic whereas the photosteady and the initial states are uniaxial.

  17. Photoinduced toxicity of PrF3 and LaF3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Pudovkin, M. S.; Zelenikhin, P. V.; Krasheninnikova, A. O.; Korableva, S. L.; Nizamutdinov, A. S.; Alakshin, E. M.; Semashko, V. V.; Safiullin, R. A.; Kadirov, M. K.

    2016-10-01

    PrF3 and LaF3 nanoparticles were synthesized by the hydrothermal method. The size distribution of these nanoparticles in the colloidal solution produced was studied by photon correlation spectroscopy. The mean diameter of the nanoparticles was 42 ± 1 nm. During the study of the toxicity of the nanoparticles, the mixture of a colloidal solution of the nanoparticles with cells to be studied was irradiated by 30-mW continuous lasers at wavelengths of 532 and 473 nm. The concentration of salmonella cells in normal saline was 106 cell/mL, while that of nanoparticles was 0.1 g/L. The cell survival percentage was 39, 34, and 20% for the irradiation times of 5, 10, and 15 min, respectively, at an optimal laser radiation power density of 0.4 W/cm at a wavelength of 532 nm. It was ascertained that LaF3 nanoparticles do not possess the property of photoinduced toxicity and the apoptosing effect. Moreover, the property of photoinduced toxicity is not shared by microparticles, in contrast to nanoparticles.

  18. The 2006-2007 Active Phase of Anomalous X-Ray Pulsar 4U 0142+61: Radiative and Timing Changes, Bursts,and Burst Spectral Features

    NASA Technical Reports Server (NTRS)

    Gavriil, Fotis P.; Dib, Rim; Kaspi, Victoria M.

    2011-01-01

    After at least 6 years of quiescence, Anomalous X-ray Pulsar (AXP) 4U 0142+61 entered an active phase in 2006 March that lasted several months and included six X-ray bursts as well as many changes in the persistent X-ray emission. The bursts, the first seen from this AXP in > 11 years of Rossi X-ray Timing Explorer monitoring, all occurred in the interval between 2006 April 6 and 2007 February 7. The burst durations ranged from 0.4 - 1.8 x 10(exp 3) s. The first five burst spectra are well modeled by blackbodies, with temperatures kT approx 2 - 9 keV. However, the sixth burst had a complicated spectrum that is well characterized by a blackbody plus two emission features whose amplitude varied throughout the burst. The most prominent feature was at 14.0 keV. Upon entry into the active phase the pulsar showed a significant change in pulse morphology and a likely timing glitch. The glitch had a total frequency jump of (1.9+/-0.4) x 10(exp -7) Hz, which recovered with a decay time of 17+/-2 days by more than the initial jump, implying a net spin-down of the pulsar. Within the framework of the magnetar model, the net spin-down of the star could be explained by regions of the superfluid that rotate. slower than the rest. The bursts, flux enhancements, and pulse morphology changes can be explained as arising from crustal deformations due to stresses imposed by the highly twisted internal magnetic field. However, unlike other AXP outbursts, we cannot account for a major twist being implanted in the magnetosphere.

  19. Diatomic Spectral Database

    National Institute of Standards and Technology Data Gateway

    SRD 114 Diatomic Spectral Database (Web, free access)   All of the rotational spectral lines observed and reported in the open literature for 121 diatomic molecules have been tabulated. The isotopic molecular species, assigned quantum numbers, observed frequency, estimated measurement uncertainty, and reference are given for each transition reported.

  20. Hydrocarbon Spectral Database

    National Institute of Standards and Technology Data Gateway

    SRD 115 Hydrocarbon Spectral Database (Web, free access)   All of the rotational spectral lines observed and reported in the open literature for 91 hydrocarbon molecules have been tabulated. The isotopic molecular species, assigned quantum numbers, observed frequency, estimated measurement uncertainty and reference are given for each transition reported.

  1. Spectral collocation methods

    NASA Technical Reports Server (NTRS)

    Hussaini, M. Y.; Kopriva, D. A.; Patera, A. T.

    1987-01-01

    This review covers the theory and application of spectral collocation methods. Section 1 describes the fundamentals, and summarizes results pertaining to spectral approximations of functions. Some stability and convergence results are presented for simple elliptic, parabolic, and hyperbolic equations. Applications of these methods to fluid dynamics problems are discussed in Section 2.

  2. Triatomic Spectral Database

    National Institute of Standards and Technology Data Gateway

    SRD 117 Triatomic Spectral Database (Web, free access)   All of the rotational spectral lines observed and reported in the open literature for 55 triatomic molecules have been tabulated. The isotopic molecular species, assigned quantum numbers, observed frequency, estimated measurement uncertainty and reference are given for each transition reported.

  3. XANES spectral changes for discotic liquid crystals of bis[1,2-bis(3,4-dioctyloxyphenyl) ethanedione dioximato]Ni(II)

    NASA Astrophysics Data System (ADS)

    Yokomizo, Mitsutoshi; Kurisaki, Tsutomu; Yamaguchi, Toshio; Wakita, Hisanobu; Oka-Inagaki, Yoshio; Ohta, Kazuchika

    The one-dimensional stacking structures of a liquid crystal Ni complex- [1,2-bis(3,4-dialkoxyphenyl)ethanedione dioximato]Ni(II), [Ni{(C8O)4dpg}2],which shows thermochromism, (see Fig. 1) have been investigated over a temperature range from room temperature to 220°C by analyzing X-ray absorption near-edge structure (XANES) spectra together with a DV-X[alpha] molecular orbital calculation. The thermochromic character of the complex is discussed through the structural change with temperature in Ni--Ni and Ni to ligand atom interactions.

  4. Spectral Properties and Dynamics of Gold Nanorods Revealed by EMCCD Based Spectral-Phasor Method

    PubMed Central

    Chen, Hongtao; Digman, Michelle A.

    2015-01-01

    Gold nanorods (NRs) with tunable plasmon-resonant absorption in the near-infrared region have considerable advantages over organic fluorophores as imaging agents. However, the luminescence spectral properties of NRs have not been fully explored at the single particle level in bulk due to lack of proper analytic tools. Here we present a global spectral phasor analysis method which allows investigations of NRs' spectra at single particle level with their statistic behavior and spatial information during imaging. The wide phasor distribution obtained by the spectral phasor analysis indicates spectra of NRs are different from particle to particle. NRs with different spectra can be identified graphically in corresponding spatial images with high spectral resolution. Furthermore, spectral behaviors of NRs under different imaging conditions, e.g. different excitation powers and wavelengths, were carefully examined by our laser-scanning multiphoton microscope with spectral imaging capability. Our results prove that the spectral phasor method is an easy and efficient tool in hyper-spectral imaging analysis to unravel subtle changes of the emission spectrum. Moreover, we applied this method to study the spectral dynamics of NRs during direct optical trapping and by optothermal trapping. Interestingly, spectral shifts were observed in both trapping phenomena. PMID:25684346

  5. Spectral properties and dynamics of gold nanorods revealed by EMCCD-based spectral phasor method.

    PubMed

    Chen, Hongtao; Gratton, Enrico; Digman, Michelle A

    2015-04-01

    Gold nanorods (NRs) with tunable plasmon-resonant absorption in the near-infrared region have considerable advantages over organic fluorophores as imaging agents due to their brightness and lack of photobleaching. However, the luminescence spectral properties of NRs have not been fully characterized at the single particle level due to lack of proper analytic tools. Here, we present a spectral phasor analysis method that allows investigations of NRs' spectra at single particle level showing the spectral variance and providing spatial information during imaging. The broad phasor distribution obtained by the spectral phasor analysis indicates that spectra of NRs are different from particle to particle. NRs with different spectra can be identified in images with high spectral resolution. The spectral behaviors of NRs under different imaging conditions, for example, different excitation powers and wavelengths, were revealed by our laser-scanning multiphoton microscope using a high-resolution spectrograph with imaging capability. Our results prove that the spectral phasor method is an easy and efficient tool in hyper-spectral imaging analysis to unravel subtle changes of the emission spectrum. We applied this method to study the spectral dynamics of NRs during direct optical trapping and by optothermal trapping. Interestingly, different spectral shifts were observed in both trapping phenomena.

  6. Assessment of MSS spectral indexes for monitoring arid rangeland

    NASA Technical Reports Server (NTRS)

    Musick, H. B.

    1983-01-01

    The utility of MSS spectral indexes for monitoring arid rangeland vegetation was tested by determining correlations between spectral indexes and vegetation parameters and by examining retrospective MSS data to determine if vegetation change could be detected and measured using spectral indexes. MSS Band 5, albedo, and the Kauth-Thomas Brightness component appear to be useful for monitoring total vegetation cover. Multiseasonal green vegetation indexes could be used to estimate changes in the shrub/grass ratio. In retrospective monitoring, spectral index change appeared to be offset from true change, indicating that the methods used to standardize data sets for differences in solar elevation and sensor radiometric response were not completely successful.

  7. Valence-electron spectral change and charge transfer mechanism of CaSi 2 during CaSi 2H 2O reaction

    NASA Astrophysics Data System (ADS)

    Abe, S.; Nakayama, H.; Nishino, T.; Iida, S.

    1997-04-01

    The changes in the valence electron states of CaSi 2 during the chemical reaction with H 2O have been investigated by Auger valence electron spectroscopy (AVES). The drastic changes in the valence electron spectra of 3s and 3p states, which are caused by the oxidization of the Si atoms in CaSi 2, were observed in Si[2s, 2p, V] spectra for CaSi 2 after the reaction. In particular, the Si[2s, 2p, V] spectra of CaSi 2 samples reacted with H 2O at 60 or 80°C for 3 h were almost similar to that of SiO 2. The peak shift of Ca[2p, 3p, 3p] Auger transition toward the lower energy side has been observed, suggesting the formation of bonds between Ca 3p and O orbitals. New peaks due to CaO or CaOH bonds also appeared in the valence electron region of Ca[2p, 3p, V] Auger transition. The charge transfer and the chemical-bond formation can be well demonstrated by AVES during the CaSi 2H 2O reaction.

  8. The 2006-2007 Active Phase Of Anomalous X-Ray Pulsar 4U 0142+61: Radiative and Timing Changes, Bursts, and Burst Spectral Features

    NASA Technical Reports Server (NTRS)

    Gavril, Fotis P.; Dib, Rim; Kaspi, Victoria M.

    2009-01-01

    After at least 6 years of quiescence, Anomalous X-ray Pulsar (AXP) 4U 0142+61 entered an active phase in 2006 March that lasted several months and included six X-ray bursts as well as many changes in the persistent X-ray emission. The bursts, the first seen from this AXP in >11 years of Rossi X-ray Timing Explorer monitoring, all occurred in the interval between 2006 April 6 and 2007 February 7. The burst durations ranged from 8-3x10(exp 3)s. The first five burst spectra are well modeled by blackbodies, with temperatures kT approx. 2 - 6 keV. However, the sixth burst had a complicated spectrum that is well characterized by a blackbody plus three emission features whose amplitude varied throughout the burst. The most prominent feature was at 14.0 keV. Upon entry into the active phase the pulsar showed a significant change in pulse morphology and a likely timing glitch. The glitch had a total frequency jump of (1.9+/-0.4)x10(exp -7) Hz, which recovered with a decay time of 17+/-2 days by more than the initial jump, implying a net spin-down of the pulsar. We discuss these events in the context of the magnetar model.

  9. Photoinduced charge generation rates in soluble P3HT : PCBM nano-aggregates predict the solvent-dependent film morphology

    NASA Astrophysics Data System (ADS)

    Roy, Palas; Jha, Ajay; Dasgupta, Jyotishman

    2016-01-01

    The device efficiency of bulk heterojunction (BHJ) solar cells is critically dependent on the nano-morphology of the solution-processed polymer : fullerene blend. Active control on blend morphology can only emanate from a detailed understanding of solution structures during the film casting process. Here we use photoinduced charge transfer (CT) rates to probe the effective length scale of the pre-formed solution structures and their energy disorder arising from a mixture of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in three different organic solvents. The observed solvent-dependent ultrafast biphasic rise of the transient polaron state in solution along with changes detected in the C&z.dbd;C stretching frequency of bound PCBM provides direct evidence for film-like P3HT : PCBM interfaces in solution. Using the diffusive component of the charge transfer rate, we deduce ~3-times larger functional nano-domain size in toluene than in chlorobenzene thereby correctly predicting the relative polymer nanofiber widths observed in annealed films. We thus provide first experimental evidence for the postulated polymer : fullerene : solvent ternary phase that seeds the eventual morphology in spin-cast films. Our work motivates the design of new chemical additives to tune the grain size of the evolving polymer : fullerene domains within the solution phase.The device efficiency of bulk heterojunction (BHJ) solar cells is critically dependent on the nano-morphology of the solution-processed polymer : fullerene blend. Active control on blend morphology can only emanate from a detailed understanding of solution structures during the film casting process. Here we use photoinduced charge transfer (CT) rates to probe the effective length scale of the pre-formed solution structures and their energy disorder arising from a mixture of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in three

  10. Spectral imagery collection experiment

    NASA Astrophysics Data System (ADS)

    Romano, Joao M.; Rosario, Dalton; Farley, Vincent; Sohr, Brian

    2010-04-01

    The Spectral and Polarimetric Imagery Collection Experiment (SPICE) is a collaborative effort between the US Army ARDEC and ARL for the collection of mid-wave and long-wave infrared imagery using hyperspectral, polarimetric, and broadband sensors. The objective of the program is to collect a comprehensive database of the different modalities over the course of 1 to 2 years to capture sensor performance over a wide variety of adverse weather conditions, diurnal, and seasonal changes inherent to Picatinny's northern New Jersey location. Using the Precision Armament Laboratory (PAL) tower at Picatinny Arsenal, the sensors will autonomously collect the desired data around the clock at different ranges where surrogate 2S3 Self-Propelled Howitzer targets are positioned at different viewing perspectives at 549 and 1280m from the sensor location. The collected database will allow for: 1) Understand of signature variability under the different weather conditions; 2) Development of robust algorithms; 3) Development of new sensors; 4) Evaluation of hyperspectral and polarimetric technologies; and 5) Evaluation of fusing the different sensor modalities. In this paper, we will present the SPICE data collection objectives, the ongoing effort, the sensors that are currently deployed, and how this work will assist researches on the development and evaluation of sensors, algorithms, and fusion applications.

  11. Directional photoinduced electron transfer in paraquat silicate thin films containing entrapped ruthenium(II)-tris(bathophenanthroline-disulfonate).

    PubMed

    Trammell, Scott A; Tsoi, Stanislav; Martin, Brett; Melde, Brian J; Moore, Martin M; Dressick, Walter J

    2011-10-28

    We have demonstrated directional photoinduced electron transfer in paraquat silicate thin films containing entrapped ruthenium(II)-tris(bathophenanthroline-disulfonate (RuBPS). The films were made by electrochemically-induced hydrolysis of a silane analogue of paraquat with ruthenium(II)-tris(bathophenanthroline-disulfonate as its ion pair.

  12. Photo-induced hydrogen production in a helical peptide incorporating a [FeFe] hydrogenase active site mimic.

    PubMed

    Roy, Anindya; Madden, Christopher; Ghirlanda, Giovanna

    2012-10-11

    There is growing interest in the development of hydrogenase mimics for solar fuel production. Here, we present a bioinspired mimic designed by anchoring a diiron hexacarbonyl cluster to a model helical peptide via an artificial dithiol amino acid. The [FeFe]-peptide complex catalyses photo-induced production of hydrogen in water.

  13. Photoinduced Graft-Polymerization of Acrylic Acid on Polyethylene and Polypropylene Surfaces: Comparative Study Using IR-ATR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Gorbachev, A. A.; Tretinnikov, O. N.; Shkrabatovskaya, L. V.; Prikhodchenko, L. K.

    2014-11-01

    Photoinduced graft-polymerization of acrylic acid on the surface of polyethylene and polypropylene films containing a photoinitiator pre-adsorbed from a thin layer of non-de-aerated aqueous monomer solution was investigated. Data about the monomer conversion and grafting depth as functions of the UV irradiation time and polymer nature were obtained using IR-ATR spectroscopy.

  14. Facile Synthesis of Stapled, Structurally Reinforced Peptide Helices via A Photoinduced Intramolecular 1,3-Dipolar Cycloaddition Reaction†

    PubMed Central

    Madden, Michael M.; Vera, Claudia I. Rivera; Song, Wenjiao; Lin, Qing

    2009-01-01

    We report the first use of a photoinduced 1,3-dipolar cycloaddition reaction in “stapling” peptide side chains to reinforce a model peptide helical structure with moderate to excellent yields. The resulting pyrazoline “staplers” exhibit unique fluorescence useful in a cell permeability study. PMID:19753366

  15. Towards efficient photoinduced charge separation in carbon nanodots and TiO2 composites in the visible region.

    PubMed

    Sun, Mingye; Qu, Songnan; Ji, Wenyu; Jing, Pengtao; Li, Di; Qin, Li; Cao, Junsheng; Zhang, Hong; Zhao, Jialong; Shen, Dezhen

    2015-03-28

    In this work, photoinduced charge separation behaviors in non-long-chain-molecule-functionalized carbon nanodots (CDs) with visible intrinsic absorption (CDs-V) and TiO2 composites were investigated. Efficient photoinduced electron injection from CDs-V to TiO2 with a rate of 8.8 × 10(8) s(-1) and efficiency of 91% was achieved in the CDs-V/TiO2 composites. The CDs-V/TiO2 composites exhibited excellent photocatalytic activity under visible light irradiation, superior to pure TiO2 and the CDs with the main absorption band in the ultraviolet region and TiO2 composites, which indicated that visible photoinduced electrons and holes in such CDs-V/TiO2 composites could be effectively separated. The incident photon-to-current conversion efficiency (IPCE) results for the CD-sensitized TiO2 solar cells also agreed with efficient photoinduced charge separation between CDs-V and the TiO2 electrode in the visible range. These results demonstrate that non-long-chain-molecule-functionlized CDs with a visible intrinsic absorption band could be appropriate candidates for photosensitizers and offer a new possibility for the development of a well performing CD-based photovoltaic system.

  16. Mechanistic insights into the photoinduced charge carrier dynamics of BiOBr/CdS nanosheet heterojunctions for photovoltaic application.

    PubMed

    Jia, Huimin; Zhang, Beibei; He, Weiwei; Xiang, Yong; Zheng, Zhi

    2017-03-02

    The rational design of high performance hetero-structure photovoltaic devices requires a full understanding of the photoinduced charge transfer mechanism and kinetics at the interface of heterojunctions. In this paper, we intelligently fabricated p-BiOBr/n-CdS heterojunctions with perfect nanosheet arrays by using a facile successive ionic layer adsorption and reaction and chemical bath deposition methods at low temperature. A BiOBr/CdS heterojunction based solar cell has been fabricated which exhibited enhanced photovoltaic responses. Assisted by the surface photovoltage (SPV), transient photovoltage (TPV) and Kelvin probe technique, the photoinduced charge transfer dynamics on the BiOBr nanosheet and p-BiOBr/n-CdS interface were systematically investigated. It was found that the BiOBr/CdS nanosheet array heterojunctions were more efficient in facilitating charge carrier separation than both bare BiOBr and CdS films. The mechanism underlying the photoinduced charge carrier transfer behaviour was unravelled by allying the energy band of BiOBr/CdS p-n junctions from both the interfacial electric field and surface electric field. In addition, the CdS loading thickness in the p-BiOBr/n-CdS heterojunction and the incident wavelength affected greatly the transfer behavior of photoinduced charges, which was of great value for design of photovoltaic devices.

  17. PHOTO-INDUCED POLYCYCLIC AROMATIC HYDROCARBON TOXIC POTENTIALS OF NEAR SHORE LARVAL FISH HABITAT IN THE GREAT LAKES, USA

    EPA Science Inventory

    Photo-induced toxicity (PIT) of polycyclic aromatic hydrocarbons (PAH) has been documented in laboratory studies for both invertebrate and vertebrate aquatic organisms. PIT has not been verified in field studies for larval fish to date. Filtered water samples and larval fish were...

  18. The investigation of photo-induced chemiluminescence on Co2+-doped TiO2 nanoparticles and its analytical application.

    PubMed

    Li, Guixin; Nan, Hongyan; Zheng, Xingwang

    2009-07-01

    A novel space- and time-resolved photo-induced chemiluminescence (PICL) analytical method was developed based on the photocatalysis of the Co2+-doped TiO2 nanoparticles. The PICL reaction procedure under the photocatalysis of Co2+-doped TiO2 nanoparticles was investigated using cyclic voltammetry and potentiometry. Meanwhile, the effect of the electrical double layer outside the Co2+-doped TiO2 nanoparticles on the PICL was investigated by contrasting with the Co2+-doped TiO2-SiO2 core-shell nanoparticles. Significantly, the CL intensity increased apparently and the time of the CL was prolonged in the presence of procaterol hydrochloride because the mechanism of the enhanced PICL reaction may be modified. The route of the PICL was changed due to the participation of the procaterol hydrochloride enriched at the surface of the Co2+-doped TiO2-SiO2 in the PICL reaction, which prolonged the time of the CL reaction and resulted in the long-term PICL. The analytical characteristics of the proposed in-situ PICL method were investigated using the procaterol hydrochloride as the model analyte. The investigation results showed that this new PICL analytical method offered higher sensitivity to the analysis of the procaterol hydrochloride and the PICL intensity was linear with the concentration of the procaterol hydrochloride in the range from ca. 2.0 x 10(-10) to 1.0 x 10(-8) g mL(-1).

  19. The prospects for detecting spectral shifts due to satellite sensor aging

    NASA Technical Reports Server (NTRS)

    Suits, G.; Malila, W.; Weller, T.

    1988-01-01

    Along with responsivity changes due to sensor aging, there may be concurrent spectral changes. A field-measurement approach for detecting postlaunch spectral changes is described. For illustration, one hypothetical model of change (spectral band shift) is explored through simulation for five satellite sensors. Two different types of natural terrain - vegetation and bare soil - are used as test targets.

  20. Changes in the spectral composition of animal-brain electrical activity under the influence of nonthermal millimeter-wave radiation on acupuncture points

    SciTech Connect

    Khramov, R.N.; Vorob`ev, V.V.

    1994-07-01

    The frequency spectra (0-26 Hz) of electrograms (EG) of the preoptic region of the hypothalamus were studied in chronic experiments on nine awake rabbits under the influence of nonthermal millimeter-bank (55-75 GHz) electromagnetic fields on various acupuncture points: (I) the auricular {open_quotes}heart{close_quotes} point (after F. G. Portnov); (II) the cranial acupoint (TR-20; the {open_quotes}hypothalamus{close_quotes} point after R. Voll); and (III) the {open_quotes}longevity{close_quotes} acupoint (E-36). Irradiation of point I was accompanied by significant suppression of hypothalamic electrical activity at 5 and 16 Hz and enhancement at 7-8, 12, and 26 Hz. Irradiation of point II, and III were, respectively, 31%, 21%, and 5% (p < 0.05, U-criterion). These results suggest that acupuncture points I and II are more sensitive to millimeter-band radiation than is point III. The presence of individual characteristics of the effects and their change after stress to sign inversion were shown in rat experiments in which the acupuncture points were irradiated.

  1. Quantitative Raman spectral changes of the differentiation of mesenchymal stem cells into islet-like cells by biochemical component analysis and multiple peak fitting

    NASA Astrophysics Data System (ADS)

    Su, Xin; Fang, Shaoyin; Zhang, Daosen; Zhang, Qinnan; He, Yingtian; Lu, Xiaoxu; Liu, Shengde; Zhong, Liyun

    2015-12-01

    Mesenchymal stem cells (MSCs) differentiate into islet-like cells, providing a possible solution for type I diabetes treatment. To search for the precise molecular mechanism of the directional differentiation of MSC-derived islet-like cells, biomolecular composition, and structural conformation information during MSC differentiation, is required. Because islet-like cells lack specific surface markers, the commonly employed immunostaining technique is not suitable for their identification, physical separation, and enrichment. Combining Raman spectroscopic data, a fitting accuracy-improved biochemical component analysis, and multiple peaks fitting approach, we identified the quantitative biochemical and intensity change of Raman peaks that show the differentiation of MSCs into islet-like cells. Along with increases in protein and glycogen content, and decreases in deoxyribonucleic acid and ribonucleic acid content, in islet-like cells relative to MSCs, it was found that a characteristic peak of insulin (665 cm-1) has twice the intensity in islet-like cells relative to MSCs, indicating differentiation of MSCs into islet-like cells was successful. Importantly, these Raman signatures provide useful information on the structural and pathological states during MSC differentiation and help to develop noninvasive and label-free Raman sorting methods for stem cells and their lineages.

  2. Molecular modeling and spectral comparison for the change in methyl position of nitrophenol compounds 2-methyl-4-nitrophenol and 3-methyl-4-nitrophenol: a density functional theoretical study.

    PubMed

    Siva Priya, M; Usha Rani, N; James, C

    2013-04-15

    FT-IR and FT-Raman spectra of 2-methyl-4-nitrophenol (PNOC) and 3-methyl-4-nitrophenol (PNMC) were recorded and analyzed in the solid phase in the region 4000-400 cm(-1) and 3500-50 cm(-1) respectively. Molecular modeling of the compounds PNOC and PNMC were done by the density functional theoretical (DFT) method using Becke's three parameter exchange functional combined with the Lee-Yang-Parr correlation functional with 6-31G(d) as basis set. Vibrational assignments of the two compounds have been carried out with the help of Normal coordinate analyses (NCA) followed by the Scaled Quantum Mechanical Force Field calculations (SQMFF). Intra-molecular charge transfer and delocalization within the molecule is confirmed with the aid of natural bond orbital analysis (NBO). PNOC and PNMC are similar compounds with same functional groups, only the position of the methyl group is different. The effect of the position change of the methyl group was interpreted with the vibrational spectra.

  3. Experimental investigation of change of energy of infragavity waves in dependence on spectral characteristics of an irregular wind waves in coastal zone

    NASA Astrophysics Data System (ADS)

    Saprykina, Yana; Divinskii, Boris

    2013-04-01

    An infragravity waves are long waves with periods of 20 - 300 s. Most essential influence of infragarvity waves on dynamic processes is in a coastal zone, where its energy can exceed the energy of wind waves. From practical point of view, the infragravity waves are important, firstly, due to their influence on sand transport processes in a coastal zone. For example, interacting with group structure of wind waves the infragravity waves can define position of underwater bars on sandy coast. Secondly, they are responsible on formation of long waves in harbors. Main source of infragravity waves is wave group structure defined by sub-nonlinear interactions of wind waves (Longuet-Higgins, Stewart, 1962). These infragravity waves are bound with groups of wind waves and propagate with wave group velocity. Another type of infragravity waves are formed in a surf zone as a result of migration a wave breaking point (Symonds, et al., 1982). What from described above mechanisms of formation of infragravity waves prevails, till now it is unknown. It is also unknown how energy of infragravity waves depends on energy of input wind waves and how it changes during nonlinear wave transformation in coastal zone. In our work on the basis of the analysis of data of field experiment and numerical simulation a contribution of infragravity waves in total wave energy in depending on integral characteristics of an irregular wave field in the conditions of a real bathymetry was investigated. For analysis the data of field experiment "Shkorpilovtsy-2007" (Black sea) and data of numerical modeling of Boussinesq type equation with extended dispersion characteristics (Madsen et al., 1997) were used. It was revealed that infragravity waves in a coastal zone are defined mainly by local group structure of waves, which permanently changes due to nonlinearity, shoaling and breaking processes. Free infragravity waves appearing after wave breaking exist together with bound infragravity waves. There are

  4. Heart cycle-related effects on event-related potentials, spectral power changes, and connectivity patterns in the human ECoG.

    PubMed

    Kern, Markus; Aertsen, Ad; Schulze-Bonhage, Andreas; Ball, Tonio

    2013-11-01

    The perception of one's own heartbeat is a fundamental interoceptive process that involves cortical and subcortical structures. Yet, the precise spatiotemporal neuronal activity patterns underlying the cortical information processing have remained largely elusive. Although the high temporal and spatial resolution of electrocorticographic (ECoG) recordings is increasingly being exploited in functional neuroimaging, it has not been used to study heart cycle-related effects. Here, we addressed the capacity of ECoG to characterize neuronal signals within the cardiac cycle, as well as to disentangle them from heart cycle-related artifacts. Based on topographical distribution and latency, we identified a biphasic potential within the primary somatosensory cortex, which likely constitutes a heartbeat-evoked potential (HEP) of neuronal origin. We also found two different types of artifacts: i) oscillatory potential changes with a frequency identical to the heart pulse rate, which probably represent pulsatility artifacts and ii) sharp potentials synchronized to the R-peak, corresponding to the onset of ventricular contraction and the cardiac field artifact (CFA) in EEG. Finally, we show that heart cycle-related effects induce pronounced phase-synchrony patterns in the ECoG and that this kind of correlation patterns, which may confound ECoG connectivity studies, can be reduced by a suitable correction algorithm. The present study is, to our knowledge, the first one to show a focally localized cortical HEP that could be clearly and consistently observed over subjects, suggesting a basic role of primary sensory cortex in processing of heart-related sensory inputs. We also conclude that taking into account and reducing heart cycle-related effects may be advantageous for many ECoG studies, and are of crucial importance, particularly for ECoG-based connectivity studies. Thus, in summary, although ECoG poses new challenges, it opens up new possibilities for the investigation of

  5. Commission 45: Spectral Classification

    NASA Astrophysics Data System (ADS)

    Giridhar, Sunetra; Gray, Richard O.; Corbally, Christopher J.; Bailer-Jones, Coryn A. L.; Eyer, Laurent; Irwin, Michael J.; Kirkpatrick, J. Davy; Majewski, Steven; Minniti, Dante; Nordström, Birgitta

    This report gives an update of developments (since the last General Assembly at Prague) in the areas that are of relevance to the commission. In addition to numerous papers, a new monograph entitled Stellar Spectral Classification with Richard Gray and Chris Corbally as leading authors will be published by Princeton University Press as part of their Princeton Series in Astrophysics in April 2009. This book is an up-to-date and encyclopedic review of stellar spectral classification across the H-R diagram, including the traditional MK system in the blue-violet, recent extensions into the ultraviolet and infrared, the newly defined L-type and T-type spectral classes, as well as spectral classification of carbon stars, S-type stars, white dwarfs, novae, supernovae and Wolf-Rayet stars.

  6. Temporal Lorentzian spectral triples

    NASA Astrophysics Data System (ADS)

    Franco, Nicolas

    2014-09-01

    We present the notion of temporal Lorentzian spectral triple which is an extension of the notion of pseudo-Riemannian spectral triple with a way to ensure that the signature of the metric is Lorentzian. A temporal Lorentzian spectral triple corresponds to a specific 3 + 1 decomposition of a possibly noncommutative Lorentzian space. This structure introduces a notion of global time in noncommutative geometry. As an example, we construct a temporal Lorentzian spectral triple over a Moyal-Minkowski spacetime. We show that, when time is commutative, the algebra can be extended to unbounded elements. Using such an extension, it is possible to define a Lorentzian distance formula between pure states with a well-defined noncommutative formulation.

  7. Adaptive spectral doppler estimation.

    PubMed

    Gran, Fredrik; Jakobsson, Andreas; Jensen, Jørgen Arendt

    2009-04-01

    In this paper, 2 adaptive spectral estimation techniques are analyzed for spectral Doppler ultrasound. The purpose is to minimize the observation window needed to estimate the spectrogram to provide a better temporal resolution and gain more flexibility when designing the data acquisition sequence. The methods can also provide better quality of the estimated power spectral density (PSD) of the blood signal. Adaptive spectral estimation techniques are known to provide good spectral resolution and contrast even when the observation window is very short. The 2 adaptive techniques are tested and compared with the averaged periodogram (Welch's method). The blood power spectral capon (BPC) method is based on a standard minimum variance technique adapted to account for both averaging over slow-time and depth. The blood amplitude and phase estimation technique (BAPES) is based on finding a set of matched filters (one for each velocity component of interest) and filtering the blood process over slow-time and averaging over depth to find the PSD. The methods are tested using various experiments and simulations. First, controlled flow-rig experiments with steady laminar flow are carried out. Simulations in Field II for pulsating flow resembling the femoral artery are also analyzed. The simulations are followed by in vivo measurement on the common carotid artery. In all simulations and experiments it was concluded that the adaptive methods display superior performance for short observation windows compared with the averaged periodogram. Computational costs and implementation details are also discussed.

  8. Thermophotovoltaic Spectral Control

    SciTech Connect

    DM DePoy; PM Fourspring; PF Baldasaro; JF Beausang; EJ Brown; MW Dashiel; KD Rahner; TD Rahmlow; JE Lazo-Wasem; EJ Gratrix; B Wemsman

    2004-06-09

    Spectral control is a key technology for thermophotovoltaic (TPV) direct energy conversion systems because only a fraction (typically less than 25%) of the incident thermal radiation has energy exceeding the diode bandgap energy, E{sub g}, and can thus be converted to electricity. The goal for TPV spectral control in most applications is twofold: (1) Maximize TPV efficiency by minimizing transfer of low energy, below bandgap photons from the radiator to the TPV diode. (2) Maximize TPV surface power density by maximizing transfer of high energy, above bandgap photons from the radiator to the TPV diode. TPV spectral control options include: front surface filters (e.g. interference filters, plasma filters, interference/plasma tandem filters, and frequency selective surfaces), back surface reflectors, and wavelength selective radiators. System analysis shows that spectral performance dominates diode performance in any practical TPV system, and that low bandgap diodes enable both higher efficiency and power density when spectral control limitations are considered. Lockheed Martin has focused its efforts on front surface tandem filters which have achieved spectral efficiencies of {approx}83% for E{sub g} = 0.52 eV and {approx}76% for E{sub g} = 0.60 eV for a 950 C radiator temperature.

  9. Spectrally selective glazings

    SciTech Connect

    1998-08-01

    Spectrally selective glazing is window glass that permits some portions of the solar spectrum to enter a building while blocking others. This high-performance glazing admits as much daylight as possible while preventing transmission of as much solar heat as possible. By controlling solar heat gains in summer, preventing loss of interior heat in winter, and allowing occupants to reduce electric lighting use by making maximum use of daylight, spectrally selective glazing significantly reduces building energy consumption and peak demand. Because new spectrally selective glazings can have a virtually clear appearance, they admit more daylight and permit much brighter, more open views to the outside while still providing the solar control of the dark, reflective energy-efficient glass of the past. This Federal Technology Alert provides detailed information and procedures for Federal energy managers to consider spectrally selective glazings. The principle of spectrally selective glazings is explained. Benefits related to energy efficiency and other architectural criteria are delineated. Guidelines are provided for appropriate application of spectrally selective glazing, and step-by-step instructions are given for estimating energy savings. Case studies are also presented to illustrate actual costs and energy savings. Current manufacturers, technology users, and references for further reading are included for users who have questions not fully addressed here.

  10. TDDFT-MD Study on Dynamics in Photoinduced Ring Opening of Benzene

    NASA Astrophysics Data System (ADS)

    Tateyama, Yoshitaka; Miyamoto, Yoshiyuki; Oyama, Norihisa; Ohno, Takahisa

    2004-03-01

    Coupled dynamics of ions and electrons in the excited states of molecular and solid benzene is investigated on the femtosecond scale by the efficient simulation scheme recently developed for the time-dependent density functional theory. Within the π arrow π excitations, any out-of-plane motion of ions is not induced in the molecular system basically. In the solid, however, we found that large swing of the C-H bonds and subsequent twist of the carbon ring takes place, leading to sp^3-like bonding of carbon ions. This swing-to-twist motion presents a plausible mechanism underlying the photoinduced ring opening in solid benzene experimentally observed under pressure. This research is partially supported by ACT-JST, and also by FSIS and Special Coordination Funds of Ministry of Education, Culture, Sports, Science and Technology of Japanese Government.

  11. Role of coherence and delocalization in photo-induced electron transfer at organic interfaces

    PubMed Central

    Abramavicius, V.; Pranculis, V.; Melianas, A.; Inganäs, O.; Gulbinas, V.; Abramavicius, D.

    2016-01-01

    Photo-induced charge transfer at molecular heterojunctions has gained particular interest due to the development of organic solar cells (OSC) based on blends of electron donating and accepting materials. While charge transfer between donor and acceptor molecules can be described by Marcus theory, additional carrier delocalization and coherent propagation might play the dominant role. Here, we describe ultrafast charge separation at the interface of a conjugated polymer and an aggregate of the fullerene derivative PCBM using the stochastic Schrödinger equation (SSE) and reveal the complex time evolution of electron transfer, mediated by electronic coherence and delocalization. By fitting the model to ultrafast charge separation experiments, we estimate the extent of electron delocalization and establish the transition from coherent electron propagation to incoherent hopping. Our results indicate that even a relatively weak coupling between PCBM molecules is sufficient to facilitate electron delocalization and efficient charge separation at organic interfaces. PMID:27605035

  12. Synthesis and Characterization of Coumarin-Containing Cyclic Polymer and Its Photoinduced Coupling/Dissociation.

    PubMed

    Li, Min; Fan, Wei; Hong, Chunyan; Pan, Caiyuan

    2015-12-01

    Cyclic polystyrene (PS) with a pendant coumarin group is prepared by the combination of atom transfer radical polymerization and "click" chemistry. Fluorescence resonance energy transfer process is observed in the fluorescence measurement of coumarin-containing PS, and cyclic PS exhibits stronger emission than that of its linear precursor. When cyclic PS is irradiated under UV light at λ = 365 nm, 8-shaped PS is achieved due to the dimerization of pendant coumarin group. Subsequently, 8-shaped PS can be divided into single macrocycle under UV irradiation at λ = 254 nm via the photocleavage of coumarin dimer. The photoinduced coupling and dissociation are monitored by UV/vis spectra and gel permeation chromatography (GPC).

  13. Protein secondary-shell interactions enhance the photoinduced hydrogen production of cobalt protoporphyrin IX.

    PubMed

    Sommer, Dayn Joseph; Vaughn, Michael David; Ghirlanda, Giovanna

    2014-12-28

    Hydrogen is an attractive fuel with potential for production scalability, provided that inexpensive, efficient molecular catalysts utilizing base metals can be developed for hydrogen production. Here we show for the first time that cobalt myoglobin (CoMyo) catalyzes hydrogen production in mild aerobic conditions with turnover number of 520 over 8 hours. Compared to free Co-protoporphyrin IX, incorporation into the myoglobin scaffold results in a 4-fold increase in photoinduced hydrogen production activity. Engineered variants in which specific histidine resides in proximity of the active site were mutated to alanine result in modulation of the catalytic activity, with the H64A/H97A mutant displaying activity 2.5-fold higher than wild type. Our results demonstrate that protein scaffolds can augment and modulate the intrinsic catalytic activity of molecular hydrogen production catalysts.

  14. Photo-induced current transient spectroscopy of single crystal Tl6I4Se

    NASA Astrophysics Data System (ADS)

    Liu, Z.; Peters, J. A.; Sebastian, M.; Kanatzidis, M. G.; Im, J.; Freeman, A. J.; Wessels, B. W.

    2014-11-01

    The compound Tl6I4Se is a promising wide band gap semiconductor for hard radiation detection at room temperature. To further improve its detection efficiency, native defects have been investigated using photo-induced current transient spectroscopy (PICTS). We observe two shallow acceptor levels with mean activation energies of 76, 175 meV, and two shallow donor defects 62, and 96 meV, respectively. No deeper donor levels are observed. The levels are attributed to native point defects. Defect capture cross sections in the range 10-21 to 10-18 cm2 were measured. The small capture cross sections are attributed to the effective screening of the defects due to a large static dielectric constant.

  15. Photoinduced DNA damage and cytotoxicity by a triphenylamine-modified platinum-diimine complex.

    PubMed

    Zhang, Zhigang; Dai, Ruihui; Ma, Jiajia; Wang, Shuying; Wei, Xuehong; Wang, Hongfei

    2015-02-01

    Many planar photosensitizers tend to self-aggregate via van der Waals interactions between π-conjugated systems. The self-aggregation of the photosensitizer may reduce the efficiency of the photosensitizer to generate singlet oxygen, thereby diminishing its photodynamic activity. Efforts have been made to improve the photodynamic activity of bis-(o-diiminobenzosemiquinonato)platinum(II) which has planar geometry by the introduction of the sterically hindered triphenylamine moiety into the ligand. Herein we report the photoinduced DNA damage and cytotoxicity by a triphenylamine-modified platinum-diimine complex in red light studied by fluorescence spectra, agarose gel assay and cell viability assay. The results suggest that the triphenylamine-modified platinum-diimine complex has better capability to generate singlet oxygen than bis-(o-diiminobenzosemiquinonato)platinum(II), and it can induce DNA damage in red light, causing high photocytotoxicity in HepG-2 cells in vitro.

  16. Photoinduced formation of peroxyl radicals in aqueous solutions of nucleobase derivatives at 77 K

    NASA Astrophysics Data System (ADS)

    Lozinova, T. A.; Lander, A. V.

    2015-05-01

    It is shown that the formation of free radicals photoinduced by near-UV irradiation at 77 K in aqueous solutions of guanosine-5'-monophosphate (GMP), adenosine (Ado), adenine (A), and thymine (T) containing NaCl (0.1 M) is intensified in the presence of O2. Signals of peroxyl radicals O{2/-·} and HO{2/·} are indicated in analyzing EPR spectra, and their overall yield is 20-40% of the total amount of the formed paramagnetic products. It is found that the concentration ratio of O{2/-·} and HO{2/·} radicals depends not only on pH of the solutions before freezing but also on the duration of irradiation and method of freezing the samples. Plausible mechanisms of the processes are discussed.

  17. Photoinduced field-assisted electron emission from dielectric-coated electrodes into gases

    NASA Astrophysics Data System (ADS)

    Josepson, R.; Laan, M.; Aarik, J.; Kasikov, A.

    2008-07-01

    A photoinduced non-self-sustained discharge in a point-plane gap at near-atmospheric pressures in nitrogen and nitrogen-oxygen mixture was studied. Molybdenum and platinum points were coated with thin layers of MgO and TiO2 of different thicknesses. Static current-voltage characteristics were recorded at different intensities of triggering light, layer thickness and gas pressure. The common regularities of current-voltage characteristics were independent of the electrode/coating combinations used. The studies showed that the field-assisted two-step model of emission describes the experimental findings. The electron emission is controlled by Schottky and Fowler-Nordheim mechanisms at the metal-dielectric interface and by a recombination of positive ions with 'hot' and free electrons near the dielectric-gas interface.

  18. Photoinduced Formation of Colloidal Silver in Nitrocellulose Solutions Containing Titanium Alkoxides

    NASA Astrophysics Data System (ADS)

    Kulak, A. I.; Branitsky, G. A.

    2016-07-01

    The study shows the possibility of photo-induced reduction of silver nitrate and formation of stable colloidal silver particles in an isopropanol-N,N-dimethylacetamide solution of titanium alkoxide (polybutyl titanate) stabilized by nitrocellulose. It is established that titanium alkoxide and the products of its partial hydrolysis in the liquid composition play the role of a photocatalyst for the reduction of silver ions; the introduction of nitric or acetic acid additives to the composition significantly increases its photosensitivity. The films deposited from the liquid composition, previously irradiated with visible or UV light, consist of hydrated titanium dioxide and nitrocellulose with incorporated colloidal silver. Thermal treatment of the films at 150-245°C leads to the decomposition of nitrocellulose and an increase in the absorption by silver particles.

  19. Photoinduced fluorescence enhancement in CdSe /ZnS quantum dot monolayers: Influence of substrate

    NASA Astrophysics Data System (ADS)

    Uematsu, Takafumi; Maenosono, Shinya; Yamaguchi, Yukio

    2006-07-01

    Photoinduced fluorescence enhancement (PFE) of CdSe /ZnS core/shell quantum dot (QD) films on SiOx substrates was investigated. The fluorescence intensity of the QD film on SiO1.9 was greatly enhanced by continuous irradiation in vacuum, while the same QD film on SiO0.6 showed a small enhancement of the fluorescence intensity. After irradiation, the rate of fluorescence decay of the QD film on SiO0.6 was smaller than that of the QD film on SiO1.9. Our results suggest that the origin of PFE derives from the photoejection of electrons into the substrate, and that the oxygen-excess-related defects work as trap sites for the electrons.

  20. Evidence for Photoinduced Insulator-to-Metal transition in B-phase vanadium dioxide

    PubMed Central

    Lourembam, James; Srivastava, Amar; La-o-vorakiat, Chan; Cheng, Liang; Venkatesan, T.; Chia, Elbert E. M.

    2016-01-01

    Ultrafast optical studies have been performed on epitaxial films of the novel B-phase of vanadium dioxide using temperature-dependent optical pump-probe technique. Signature of temperature-driven metal-to-insulator transition was distinctly observed in the ultrafast dynamics — the insulating phase showed two characteristic electronic relaxation times while the metallic phase showed only one. Beyond a threshold value of the pump fluence, the insulating state collapses into a ‘metallic-like’ phase which can be further subdivided into two regimes according to the lengths of the fast characteristic time. The first regime can be explained by lattice heating due to the optical pump; the other cannot be accounted by simple lattice heating effects alone, and thus offers evidence for a true photoinduced phase transition. PMID:27157532

  1. Inter-Fullerene Electronic Coupling Controls the Efficiency of Photoinduced Charge Generation in Organic Bulk Heterojunctions

    SciTech Connect

    Larson, Bryon W.; Reid, Obadiah G.; Coffey, David C.; Avdoshenko, Stanislav M.; Popov, Alexey A.; Boltalina, Olga V.; Strauss, Steven H.; Kopidakis, Nikos; Rumbles, Garry

    2016-09-26

    Photoinduced charge generation (PCG) dynamics are notoriously difficult to correlate with specific molecular properties in device relevant polymer:fullerene organic photovoltaic blend films due to the highly complex nature of the solid state blend morphology. Here, this study uses six judiciously selected trifluoromethylfullerenes blended with the prototypical polymer poly(3-hexylthiophene) and measure the PCG dynamics in 50 fs-500 ns time scales with time-resolved microwave conductivity and femtosecond transient absorption spectroscopy. The isomeric purity and thorough chemical characterization of the fullerenes used in this study allow for a detailed correlation between molecular properties, driving force, local intermolecular electronic coupling and, ultimately, the efficiency of PCG yield. The findings show that the molecular design of the fullerene not only determines inter-fullerene electronic coupling, but also influences the decay dynamics of free holes in the donor phase even when the polymer microstructure remains unchanged.

  2. Direct visualization of photoinduced glassy dynamics on the amorphous silicon carbide surface by STM movies

    NASA Astrophysics Data System (ADS)

    Nguyen, Duc; Nienhaus, Lea; Haasch, Richard T.; Lyding, Joseph; Gruebele, Martin

    2015-03-01

    Glassy dynamics can be controlled by light irradiation. Sub- and above-bandgap irradiation cause numerous phenomena in glasses including photorelaxation, photoexpansion, photodarkening and pohtoinduced fluidity. We used scanning tunneling microscopy to study surface glassy dynamics of amorphous silicon carbide irradiated with above- bandgap 532 nm light. Surface clusters of ~ 4-5 glass forming unit in diameter hop mostly in a two-state fashion, both without and with irradiation. Upon irradiation, the average surface hopping activity increases by a factor of 3. A very long (~1 day) movie of individual clusters with varying laser power density provides direct evidence for photoinduced enhanced hopping on the glass surfaces. We propose two mechanisms: heating and electronic for the photoenhanced surface dynamics.

  3. Photoinduced reduction of divalent mercury by quinones in the presence of formic acid under anaerobic conditions.

    PubMed

    Berkovic, Andrea M; Bertolotti, Sonia G; Villata, Laura S; Gonzalez, Mónica C; Pis Diez, Reinaldo; Mártire, Daniel O

    2012-11-01

    The laser flash photolysis technique (λ(exc)=355 nm) was used to investigate the mechanism of the HgCl(2) reduction mediated by CO(2)(-) radicals generated from quenching of the triplet states of 1,4-naphthoquinone (NQ) by formic acid. Kinetic simulations of the experimental signals support the proposed reaction mechanism. This system is of potential interest in the development of UV-A photoinduced photolytic procedures for the treatment of Hg(II) contaminated waters. The successful replacement of NQ with a commercial fulvic acid, as a model compound of dissolved organic matter, showed that the method is applicable to organic matter-containing waters without the addition of quinones.

  4. Configuration-Dependent Photoinduced Electron Transfer in Diastereomeric Naphthalene-Amino-Naphthalene Triads.

    PubMed

    Nuin, Edurne; Sastre, German; Pischel, Uwe; Andreu, Inmaculada; Miranda, Miguel A

    2015-09-07

    Novel diastereomeric triads containing two naphthalene chromophores have been designed in which an electron-donating amine moiety is covalently integrated into the connecting bridge. Photophysical studies (steady-state and time-resolved fluorescence) in solvents of different polarity have been performed. A remarkable stereodifferentiation in the intramolecular fluorescence quenching was found in acetonitrile. Laser flash photolysis gave rise to naphthalene-derived radical cations, which were also quenched by the amine with an even higher degree of stereodifferentiation. The results are in agreement with thermodynamic estimations and indicate that photoinduced electron transfer (PET) is the main quenching pathway. Furthermore, theoretical calculations have allowed us to explain the experimentally observed stereodifferentiation in PET quenching.

  5. Effect of temperature, energy gap, and distortion of potential surfaces on photoinduced intramolecular electron transfer

    SciTech Connect

    Islampour, R.; Alden, R.G.; Wu, G.Y.C.; Lin, S.H. )

    1993-07-01

    We report the quantitative examination of the effect of distortion of potential energy surfaces and the temperature effect on photoinduced intramolecular electron transfer (PIET) as a function of electronic energy gap. The results demonstrate the importance of distorted oscillators in determining the dependence of the rate of PIET on the energy gap. This phenomenon may in some cases lead to misinterpretations of experimental data, when undistorted oscillators are assumed to be involved in the PIET process. The condition for observing the linear (rather than parabolic) dependence of the ET rate will be determined using the multimode model. The inclusion of multivibrational modes in the nuclear factors results in energy gap behavior, which is markedly different from the single mode case. Finally, a comparison between PIET and internal conversion is discussed. 25 refs., 5 figs., 3 tabs.

  6. Photo-induced potential barrier in As-Se-Ge films

    NASA Astrophysics Data System (ADS)

    Katyal, S. C.; Okano, S.; Suzuki, M.; Bando, T.

    1988-05-01

    Photo-excited effects in AsSeGe and AsSeGeSn amorphous films have been studied under illumination of different light sources. AsSeGe system exhibited rectifying characteristics under illumination of the light with hν > E g, while AsSeGeSn film did not show such phenomena. The illumination of the IR light along with the light of hν > E g weakened the rectification behavior. The photovoltage and I-V characteristics results suggest the existence of "photo-induced" potential barrier in AsSeGe system, which is considered to concern the creation and destruction of neutral defect states D°.

  7. Nonlinear spectral imaging of biological tissues

    NASA Astrophysics Data System (ADS)

    Palero, J. A.

    2007-07-01

    The work presented in this thesis demonstrates live high resolution 3D imaging of tissue in its native state and environment. The nonlinear interaction between focussed femtosecond light pulses and the biological tissue results in the emission of natural autofluorescence and second-harmonic signal. Because biological intrinsic emission is generally very weak and extends from the ultraviolet to the visible spectral range, a broad-spectral range and high sensitivity 3D spectral imaging system is developed. Imaging the spectral characteristics of the biological intrinsic emission reveals the structure and biochemistry of the cells and extra-cellular components. By using different methods in visualizing the spectral images, discrimination between different tissue structures is achieved without the use of any stain or fluorescent label. For instance, RGB real color spectral images of the intrinsic emission of mouse skin tissues show blue cells, green hair follicles, and purple collagen fibers. The color signature of each tissue component is directly related to its characteristic emission spectrum. The results of this study show that skin tissue nonlinear intrinsic emission is mainly due to the autofluorescence of reduced nicotinamide adenine dinucleotide (phosphate), flavins, keratin, melanin, phospholipids, elastin and collagen and nonlinear Raman scattering and second-harmonic generation in Type I collagen. In vivo time-lapse spectral imaging is implemented to study metabolic changes in epidermal cells in tissues. Optical scattering in tissues, a key factor in determining the maximum achievable imaging depth, is also investigated in this work.

  8. Photo-induced toxicity of titanium dioxide nanoparticles to Daphnia magna under natural sunlight.

    PubMed

    Mansfield, C M; Alloy, M M; Hamilton, J; Verbeck, G F; Newton, K; Klaine, S J; Roberts, A P

    2015-02-01

    Titanium dioxide nanoparticles (TiO2 NP) are one of the most abundantly utilized nanoparticles in the world. Studies have demonstrated the ability of the anatase crystal of TiO2 NP to produce reactive oxygen species (ROS) in the presence of ultraviolet radiation (UVR), a co-exposure likely to occur in aquatic ecosystems. The goal of this study was to examine the photo-induced toxicity of anatase TiO2 NP under natural sunlight to Daphnia magna. D. magna were exposed to a range of UVR intensities and anatase TiO2 concentrations in an outdoor exposure system using the sun as the source of UVR. Different UVR intensities were achieved using UVR opaque and transparent plastics. AnataseTiO2-NP demonstrated the reciprocal relationship seen in other phototoxic compounds such as polycyclic aromatic hydrocarbons (PAHs) at higher UVR treatments. The calculated 8h LC50 of anatase TiO2 NP was 139 ppb under full intensity ambient natural sunlight, 778 ppb under 50% natural sunlight, and >500 ppm under 10% natural sunlight. Mortality was also compared between animals allowed to accumulate a body burden of anatase TiO2 for 1h and organisms whose first exposure to anatase TiO2 aqueous suspensions occurred under UVR. A significantly greater toxic effect was observed in aqueous, low body burden suspensions than that of TiO2 1h body burdens, which is dissimilar from the model presented in PAHs. Anatase TiO2 presents a unique photo-induced toxic model that is different than that of established phototoxic compounds.

  9. Photoinduced Dynamics and Toxicity of a Cancer Drug in Proximity of Inorganic Nanoparticles under Visible Light.

    PubMed

    Chaudhuri, Siddhi; Sardar, Samim; Bagchi, Damayanti; Dutta, Shreyasi; Debnath, Sushanta; Saha, Partha; Lemmens, Peter; Pal, Samir Kumar

    2016-01-18

    Drug sensitization with various inorganic nanoparticles (NPs) has proved to be a promising and an emergent concept in the field of nanomedicine. Rose bengal (RB), a notable photosensitizer, triggers the formation of reactive oxygen species under green-light irradiation, and consequently, it induces cytotoxicity and cell death. In the present study, the effect of photoinduced dynamics of RB upon complexation with semiconductor zinc oxide NPs is explored. To accomplish this, we successfully synthesized nanohybrids of RB with ZnO NPs with a particle size of 24 nm and optically characterized them. The uniform size and integrity of the particles were confirmed by high-resolution transmission electron microscopy. UV/Vis absorption and steady-state fluorescence studies reveal the formation of the nanohybrids. ultrafast picosecond-resolved fluorescence studies of RB-ZnO nanohybrids demonstrate an efficient electron transfer from the photoexcited drug to the semiconductor NPs. Picosecond-resolved Förster resonance energy transfer from ZnO NPs to RB unravel the proximity of the drug to the semiconductor at the molecular level. The photoinduced ROS formation was monitored using a dichlorofluorescin oxidation assay, which is a conventional oxidative stress indicator. It is observed that the ROS generation under green light illumination is greater at low concentrations of RB-ZnO nanohybrids compared with free RB. Substantial photodynamic activity of the nanohybrids in bacterial and fungal cell lines validated the in vitro toxicity results. Furthermore, the cytotoxic effect of the nanohybrids in HeLa cells, which was monitored by MTT assay, is also noteworthy.

  10. Optimizing organic photovoltaics using tailored heterojunctions: A photoinduced absorption study of oligothiophenes with low band gaps

    NASA Astrophysics Data System (ADS)

    Schueppel, R.; Schmidt, K.; Uhrich, C.; Schulze, K.; Wynands, D.; Brédas, J. L.; Brier, E.; Reinold, E.; Bu, H.-B.; Baeuerle, P.; Maennig, B.; Pfeiffer, M.; Leo, K.

    2008-02-01

    A power conversion efficiency of 3.4% with an open-circuit voltage of 1V was recently demonstrated in a thin film solar cell utilizing fullerene C60 as acceptor and a new acceptor-substituted oligothiophene with an optical gap of 1.77eV as donor [K. Schulze , Adv. Mater. (Weinheim, Ger.) 18, 2872 (2006)]. This prompted us to systematically study the energy- and electron transfer processes at the oligothiophene:fullerene heterojunction for a homologous series of these oligothiophenes. Cyclic voltammetry and ultraviolet photoelectron spectroscopy data show that the heterojunction is modified due to tuning of the highest occupied molecular orbital energy for different oligothiophene chain lengths, while the lowest unoccupied molecular orbital energy remains essentially fixed due to the presence of electron-withdrawing end groups (dicyanovinyl) attached to the oligothiophene. Use of photoinduced absorption (PA) allows the study of the electron transfer process at the heterojunction to C60 . Quantum-chemical calculations performed at the density functional theory and/or time-dependent density functional theory level and cation absorption spectra of diluted DCVnT provide an unambiguous identification of the transitions observed in the PA spectra. Upon increasing the effective energy gap of the donor-acceptor pair by increasing the ionization energy of the donor, photoinduced electron transfer is eventually replaced with energy transfer, which alters the photovoltaic operation conditions. The optimum open-circuit voltage of a solar cell is thus a trade-off between efficient charge separation at the interface and maximized effective gap. It appears that the open-circuit voltages of 1.0-1.1V in our solar cell devices have reached an optimum since higher voltages result in a loss in charge separation efficiency.

  11. Photo-induced electronic properties in single quantum well system: effect of excitonic lifetime

    NASA Astrophysics Data System (ADS)

    Patwari, Jayita; Ghadi, Hemant; Sardar, Samim; Singhal, Jashan; Tongbram, Binita; Shyamal, Sanjib; Bhattacharya, Chinmoy; Chakrabarti, Subhananda; Pal, Samir Kumar

    2017-01-01

    In the present study, we have established a correlation between the photo-induced electronic phenomena and excited state lifetime of the photo generated carriers in double barrier Al0.3Ga0.7As\\GaAs quantum well (QW) structures. The excited state lifetime was measured experimentally by picosecond time resolved photoluminescence spectroscopy for two samples with different well widths (5.3 nm and 16.5 nm). The faster nonradiative decay time of the narrower well can be attributed to the facile escape of electrons from well to barrier due to lower associated energy compared to that of the thicker well which resembles the simulated results of the energy level distribution. The proposed mechanism of carrier escape is further proven from the higher value of unconventional excitonic capacitance value in the thicker well, measured by impedance spectroscopy. The dependence of photo-induced capacitance on well thickness is explained by the lifetime of the excited carriers in this study. Dependence of the photo-generated capacitance (C) on externally applied bias voltage (V) was also studied to quantitatively establish a proportional relation between the carrier holding capacity of the well and the excitonic lifetime. The higher accumulation of charge and lower ground state energy of the thicker well is evident from the higher tunnelling current found for the same in the photocurrent (I) versus voltage (V) measurement. Thus the escape of electrons from the well to barrier is the key factor affecting the photo generated charge accumulation and its holding capacity which in turn influences the device performances.

  12. Ab initio spectroscopy and photoinduced cooling of the trans-stilbene molecule.

    PubMed

    Tatchen, Jörg; Pollak, Eli

    2008-04-28

    We present a theoretical study of the S(0)-->S(1) and S(0)<--S(1) vibronic spectra for trans-stilbene. Franck-Condon spectra in the harmonic approximation are generated for the complete system with 72 degrees of freedom by means of an analytic time-dependent approach accounting for Dushinsky rotations and thermal effects. The force fields are computed by means of density functional theory (DFT) and time-dependent DFT, on the one hand, and ab initio complete active space self-consistent field theory, on the other hand. The B3LYP functional shows that almost planar potential energy surface minima are found for the S(0) and S(1) state. Imposing C(2h) symmetry constraints, we obtain low-temperature high-resolution Franck-Condon spectra for both absorption and emission which are in reasonably good agreement with the experimental spectra measured by Syage et al. [J. Chem. Phys. 81, 4685 (1984)] in supersonic jets. Due to thermal population of low-energy modes, the room temperature absorption spectrum is very broad. An almost structureless band which extends over several thousand cm(-1) is obtained from the present theory and agrees with the experimental absorption band shape. Finally, within the harmonic model, we study the effect of photoexcitation on the energy distribution in the excited S(1) state. We find noticeable cooling of approximately 20 K within a frequency interval spanning from -400 to 200 cm(-1) around the 0-0 transition. This indicates that photoinduced cooling must be taken into account when considering the dynamics of the photoinduced isomerization of trans-stilbene. Moreover, this is not the final word, as anharmonicity of the low frequency modes must be taken into account to obtain a full picture which would explain both the energy dependence of the isomerization rates as well as the dependence on the pressure of an external buffer gas.

  13. Photoinduced electron transfer interaction of anthraquinones with aniline quenchers: Influence of methyl substitution in aniline donors

    NASA Astrophysics Data System (ADS)

    Sivakumar, V.; Ponnamma, Deepalekshmi; Hussein, Yasser H. A.

    2017-02-01

    Photoinduced electron transfer between triplet state of 9,10-anthraquinone (AQ) and its two derivatives: 2-chloro-9,10-anthraquinone (CAQ) and sodium anthraquinone-2-sulfonate (AQS) and ground state aniline (AN) and its dimethyl substitutions: 2,3-dimethylaniline (2,3-DMA), 2,6-dimethylaniline (2,6-DMA), 3,5-dimethylaniline (3,5-DMA) and N,N-dimethylaniline (N,N-DMA) is studied using nanosecond laser flash photolysis at room temperature. Detection of radical bands of quinone anions and aniline cations along with their formation and/or decay kinetics are used to confirm the electron transfer (ET) process. In MeCN medium, AN quenches the triplet state of CAQ (CAQT) but not the triplets AQT or AQST. However in aqueous medium, AN quenches AQST and forms radical ion pair. All the DMAs can react through ET with all the triplet quinones at different degrees of efficiency in MeCN medium. Noticeably, the ring substituted DMAs are less efficient in electron donation to AQT or AQST while the N,N-DMA shows high efficiency in donating electron to all triplet quinones in MeCN medium. Charge distribution of donor molecules, in MeCN medium is calculated using density functional theory (DFT), and shows an enhancement of electron density of the ring of N,N-DMA, making it an ideal electron donor for ET studies compared to other DMAs. This systematic selection and usage of anilines with electrochemically tunable quinones can be viewed as a working model of donor-acceptor system that can be utilized in photoinduced ET applications.

  14. Spectral reflectance relationships to leaf water stress

    NASA Technical Reports Server (NTRS)

    Ripple, William J.

    1986-01-01

    Spectral reflectance data were collected from detached snapbean leaves in the laboratory with a multiband radiometer. Four experiments were designed to study the spectral response resulting from changes in leaf cover, relative water content of leaves, and leaf water potential. Spectral regions included in the analysis were red (630-690 nm), NIR (760-900 nm), and mid-IR (2.08-2.35 microns). The red and mid-IR bands showed sensitivity to changes in both leaf cover and relative water content of leaves. The NIR was only highly sensitive to changes in leaf cover. Results provided evidence that mid-IR reflectance was governed primarily by leaf moisture content, although soil reflectance was an important factor when leaf cover was less than 100 percent. High correlations between leaf water potentials and reflectance were attributed to covariances with relative water content of leaves and leaf cover.

  15. INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Photoinduced anisotropy of the refractive index of an azopolymer with liquid-crystal properties

    NASA Astrophysics Data System (ADS)

    Andreeva, M. S.; Shmalgauzen, V. I.

    2004-01-01

    The formation of a photoinduced refractive-index grating in a photosensitive azopolymer with liquid-crystal (LC) properties is theoretically studied. Equations for photoinduced additions to the refractive index of the LC and amorphous polymers are obtained from balance equations for the distribution densities of trans- and cis-isomers of azodyes. The frequency characteristics of the response of the refractive index to a harmonic perturbation are calculated for different values of the LC order parameter.

  16. [Plant Spectral Discrimination Based on Phenological Features].

    PubMed

    Zhang, Lei; Zhao, Jian-long; Jia, Kun; Li, Xiao-song

    2015-10-01

    Spectral analysis plays a significant role onplant characteristic identification and mechanism recognition, there were many papers published on the aspects of absorption features in the spectra of chlorophyll and moisture, spectral analysis onvegetation red edge effect, spectra profile feature extraction, spectra profile conversion, vegetation leaf structure and chemical composition impacts on the spectra in past years. However, fewer researches issued on spectral changes caused by plant seasonal changes of life form, chlorophyll, leaf area index. This paper studied on spectral observation of 11 plants of various life form, plant leaf structure and its size, phenological characteristics, they include deciduous forest with broad vertical leaf, needle leaf evergreen forest, needle leaf deciduous forest, deciduous forest with broadflat leaf, high shrub with big leaf, high shrub with little leaf, deciduous forest with broad little leaf, short shrub, meadow, steppe and grass. Field spectral data were observed with SVC-HR768 (Spectra Vista company, USA), the band width covers 350-2 500 nm, spectral resolution reaches 1-4 nm. The features of NDVI, spectral maximum absorption depth in green band, and spectral maximum absorption depth in red band were measured after continuum removal processing, the mean, amplitude and gradient of these features on seasonal change profile were analyzed, meanwhile, separability research on plant spectral feature of growth period and maturation period were compared. The paper presents a calculation method of separability of vegetation spectra which consider feature spatial distances. This index is carried on analysis of the vegetation discrimination. The results show that: the spectral features during plant growth period are easier to distinguish than them during maturation period. With the same features comparison, plant separability of growth period is 3 points higher than it during maturation period. The overall separabilityof vegetation

  17. Noncomputable Spectral Sets

    NASA Astrophysics Data System (ADS)

    Teutsch, Jason

    2007-01-01

    It is possible to enumerate all computer programs. In particular, for every partial computable function, there is a shortest program which computes that function. f-MIN is the set of indices for shortest programs. In 1972, Meyer showed that f-MIN is Turing equivalent to 0'', the halting set with halting set oracle. This paper generalizes the notion of shortest programs, and we use various measures from computability theory to describe the complexity of the resulting "spectral sets." We show that under certain Godel numberings, the spectral sets are exactly the canonical sets 0', 0'', 0''', ... up to Turing equivalence. This is probably not true in general, however we show that spectral sets always contain some useful information. We show that immunity, or "thinness" is a useful characteristic for distinguishing between spectral sets. In the final chapter, we construct a set which neither contains nor is disjoint from any infinite arithmetic set, yet it is 0-majorized and contains a natural spectral set. Thus a pathological set becomes a bit more friendly. Finally, a number of interesting open problems are left for the inspired reader.

  18. Multipurpose Spectral Imager

    NASA Astrophysics Data System (ADS)

    Sigernes, Fred; Lorentzen, Dag Arne; Heia, Karsten; Svenøe, Trond

    2000-06-01

    A small spectral imaging system is presented that images static or moving objects simultaneously as a function of wavelength. The main physical principle is outlined and demonstrated. The instrument is capable of resolving both spectral and spatial information from targets throughout the entire visible region. The spectral domain has a bandpass of 12 . One can achieve the spatial domain by rotating the system s front mirror with a high-resolution stepper motor. The spatial resolution range from millimeters to several meters depends mainly on the front optics used and whether the target is fixed (static) or movable relative to the instrument. Different applications and examples are explored, including outdoor landscapes, industrial fish-related targets, and ground-level objects observed in the more traditional way from an airborne carrier (remote sensing). Through the examples, we found that the instrument correctly classifies whether a shrimp is peeled and whether it can disclose the spectral and spatial microcharacteristics of targets such as a fish nematode (parasite). In the macroregime, we were able to distinguish a marine vessel from the surrounding sea and sky. A study of the directional spectral albedo from clouds, mountains, snow cover, and vegetation has also been included. With the airborne experiment, the imager successfully classified snow cover, leads, and new and rafted ice, as seen from 10.000 ft (3.048 m).

  19. Individual Sensitivity to Spectral and Temporal Cues in Listeners with Hearing Impairment

    ERIC Educational Resources Information Center

    Souza, Pamela E.; Wright, Richard A.; Blackburn, Michael C.; Tatman, Rachael; Gallun, Frederick J.

    2015-01-01

    Purpose: The present study was designed to evaluate use of spectral and temporal cues under conditions in which both types of cues were available. Method: Participants included adults with normal hearing and hearing loss. We focused on 3 categories of speech cues: static spectral (spectral shape), dynamic spectral (formant change), and temporal…

  20. UV and fluorescence spectral changes induced by neodymium binding of N,N'-ethylenebis[2-(o-hydroxyphenolic)glycine] and N,N'-di(2-hydroxybenzyl)ethylenediamine-N,N' diacetic acid.

    PubMed

    Wang, Zhijun; Yang, Binsheng

    2006-11-01

    In 0.01 M 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (Hepes), pH 7.4 and room temperature, the binding of neodymium to N,N'-ethylenebis[2-(o-hydroxyphenolic)glycine] (EHPG), or N,N'-di(2-hydroxybenzyl)ethylenediamine-N,N' diacetic acid (HBED) had been studied from 210 to 330 nm by means of difference UV spectra. Two peaks at 240 and 292 nm appear in difference UV spectra after neodymium binding to EHPG or HBED. The 1:1 stable complex can be confirmed from spectral titration curves. The molar extinction coefficient of Nd-EHPG and Nd-HBED complexes are Deltaepsilon(Nd-EHPG)=(12.93+/-0.21) x 10(3)cm(-1)M(-1), Deltaepsilon(Nd-HBED)=(14.45+/-0.51) x 10(5)cm(-1)M(-1) at 240 nm, respectively. Using EDTA as a competitor, the conditional equilibrium constants of the complexes are logK(Nd-EHPG)=11.89+/-0.09 and logK(Nd-HBED)=12.19+/-0.15, respectively. At the same conditions, fluorescence measurements show that neodymium binding to EHPG leads to a quenching of the fluorescence of EHPG at near 310 nm. However, there is no obvious fluorescence change of HBED at 318 nm with the binding of neodymium to HBED.