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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 452-454 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the laser action of pyrromethene 567 incorporated into polymeric matrices and pumped longitudinally with the green line of a copper-vapor laser. When the dye was dissolved in a copolymer of methyl methacrylate and pentaerythritol triacrylate, 290 mW average power at 1 kHz (37% lasing efficiency) was obtained. The laser output decreased to 150 mW after 30 min irradiation time (1.8×106 shots) and to 32 mW after 70 min of operation (4.2×106 shots). Output power of up to 1 W at 6.2 kHz was obtained for short periods of time. Polymeric matrices incorporating rhodamine 6G were also studied. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 8902-8906 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ketene (CH2CO) cooled in a supersonic free jet is photodissociated by a tunable pulsed laser in the energy range from 1460 to 2900 cm−1 above the threshold for singlet methylene CH2(a˜ 1A1) production. By scanning the 1CH2 probe laser wavelength, the CH2 laser-induced fluorescence (LIF) excitation spectrum is recorded and the 1CH2(0,1,0), (0,2,0), and (1,0,0) product state rotational distributions determined. As observed previously for the (0,0,0) state, the rotational state distributions of vibrationally excited methylene are in good agreement with phase space theory (PST) for excess energies less than 200 cm−1 above the appearance threshold of each vibrational state probed. For higher excess energies, 1CH2(0,1,0) and (0,2,0) rotational distributions like those for (0,0,0) are substantially colder than the statistical distribution given by PST. The quantum yields of vibrationally excited states are determined at several excess energies above the singlet threshold. These values are larger than predicted by PST and match values predicted by variational Rice–Ramsperger–Kassel–Marcus (RRKM) theory and by the separate statistical ensembles (SSE) method.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 8890-8901 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ketene (CH2CO) cooled in a supersonic free jet is photodissociated by a tunable pulsed laser in the energy range from the threshold for production of CH2(a˜ 1A1)(0,0,0)+CO(X˜ 1Σ+) to 2900 cm−1 above. By scanning the 1CH2 probe laser wavelength, the CH2 laser-induced fluorescence spectrum is recorded and the 1CH2 product state distributions determined. The appearance thresholds and yield curves of individual 1CH2 rotational states are obtained by scanning the photolysis laser frequency with a fixed 1CH2 probe laser frequency. The yield curves, or photofragment excitation (PHOFEX) spectra, exhibit sharp steps spaced by the CO rotational term values. PHOFEX yield curves combined with the distribution data demonstrate that the ketene absorption cross section is constant within 10% over the 0–1000 cm−1 range of the PHOFEX spectra. PHOFEX curves up to 200 cm−1 and rotational state distributions for singlet methylene at 50, 100, and 170 cm−1 above its threshold are in good agreement with phase space theory (PST) calculations. The lowest energy methylene rotational states of + and − symmetry are formed in the ratio predicted by phase space theory at all energies. States of mixed singlet/triplet parentage are populated with equal probability for triplet characters ranging from 30% to 70%. For energies greater than 300 cm−1 above the threshold, the 1CH2 rotational distribution is substantially colder than the statistical distribution given by PST. These differences increase with excess energy above the singlet threshold. In this energy range, the dynamics of motion between the transition state and separated product fragments is in neither the adiabatic nor the statistical limit though the data do suggest that motion may well be adiabatic for molecules fragmenting to yield the lowest energy rotational states of ortho methylene.
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 305-307 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the lasing action of modified dipyrromethene BF2 complexes in air-equilibrated liquid solutions. All recent dyes share a common chromophore core and were dissolved in apolar, polar nonprotic, and polar protic solvents. When pumped transversely at 534 nm, nearly solvent-independent laser emission was obtained with efficiencies well over 40% in most cases. Highest lasing efficiency was 59%. Under continuous ultraviolet irradiation some of these dyes demonstrated improved photostability as compared with commercial dye pyrromethene 567. © 2001 American Institute of Physics.
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  • 5
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
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  • 6
    ISSN: 1432-0649
    Keywords: PACS: 42.55Mv; 42.55Rz; 42.70Hj; 42.70Jk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Laser performance of pyrromethene 567 (PM567) dye dissolved in pure poly(methyl methacrylate) homopolymer and its copolymers with 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 1-vinyl-2-pyrrolidone, 2-phenoxyethyl acrylate, and 2,2,2-trifluoromethyl methacrylate has been investigated. The chosen monomers were selected to mimic solvents used in a previous study on the photophysical and lasing properties of PM567 in liquid solution in order to establish correlations between the lasing properties of PM567 in liquid and solid solutions. The vol/vol proportion of the different comonomers in each copolymer formulation was systematically varied, and the effect of each composition on the lasing properties of PM567 was evaluated. The laser samples were transversely pumped at 534 nm with 5.5-mJ pulses from a frequency-doubled Q-switched Nd:KGW laser. Lasing efficiencies of up to 30% and good photostabilities, with a drop of the initial laser output of 20% after 10000 pump pulses in some of the solid samples, were demonstrated.
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  • 7
    ISSN: 0992-7689
    Keywords: Atmospheric composition and structure (transmission and scattering of radiation) ; Meteorology and atmospheric dynamics (radiative process)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Since the discovery of the ozone depletion in Antarctic and the globally declining trend of stratospheric ozone concentration, public and scientific concern has been raised in the last decades. A very important consequence of this fact is the increased broadband and spectral UV radiation in the environment and the biological effects and heath risks that may take place in the near future. The absence of widespread measurements of this radiometric flux has lead to the development and use of alternative estimation procedures such as the parametric approaches. Parametric models compute the radiant energy using available atmospheric parameters. Some parametric models compute the global solar irradiance at surface level by addition of its direct beam and diffuse components. In the present work, we have developed a comparison between two cloudless sky parametrization schemes. Both methods provide an estimation of the solar spectral irradiance that can be integrated spectrally within the limits of interest. For this test we have used data recorded in a radiometric station located at Granada (37.180°N, 3.580°W, 660 m a.m.s.l.), an inland location. The database includes hourly values of the relevant variables covering the years 1994/95. The performance of the models has been tested in relation to their predictive capability of global solar irradiance in the UV range (290/385 nm). After our study, it appears that information concerning the aerosol radiative effects is fundamental in order to obtain a good estimation. The original version of SPCTRAL2 provides estimates of the experimental values with negligible mean bias deviation. This suggests not only the appropriateness of the model but also the convenience of the aerosol features fixed in it to Granada conditions. SMARTS2 model offers increased flexibility concerning the selection of different aerosol models included in the code and provides the best results when the selected models are those considered as urban. Although SMARTS2 provide slightly worse results, both models give estimates of solar ultraviolet irradiance with mean bias deviation below 5%, and root mean square deviation close to experimental errors.
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  • 8
    ISSN: 1365-2133
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Summary Background It is widely accepted that CD40 plays a critical role in the regulation of immune response. However, the significance of CD40 expression on normal human keratinocytes is only partially known. Objectives To perform a morphological re-examination of the role of CD40 on the differentiation of human keratinocytes and remodelling of the epidermis. Methods Keratinocytes were grown on fibroblasts transfected with the CD40 ligand (CD40L) to investigate the formation of epidermal sheets in culture under the influence of the CD40L. Control experiments were carried out using the same cells but transfected with CD32. Further, three specific anti-CD40 monoclonal antibodies were used as soluble agonists to analyse the effect of CD40 ligation on keratinocyte differentiation. Results Epidermal sheets developing from keratinocytes cocultured with fibroblasts transfected with CD40L but not with CD32 showed an up to 50% reduction in thickness compared with control sheets. This change depended mostly on cellular flattening and a decrease in the number of cell layers, and was coincident with a transient decrease in cell surface CD40 immunoreactivity. On the other hand, normal epidermis, and freshly isolated and cultured keratinocytes revealed a predominant CD40+/Ki-67– phenotype that was demonstrated by double immunocytochemistry. Consistent with these observations, keratinocytes primed with interferon-γ responded to the three soluble agonists, but not to control IgG1, producing immunoreactive (pro)filaggrin and displaying morphological changes in shape and size equivalent to those seen in differentiated cells. Conclusions As a whole, our findings provide evidence that CD40+ keratinocytes represent a poorly differentiated population, not actively engaged in the cell cycle, which under specific stimulation is committed towards terminal differentiation.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 3159-3166 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the laser action of pyrromethene 567 (PM567) incorporated into copolymers of methyl methacrylate (MMA) with different methacrylic and acrylic cross-linking monomers: ethyleneglycol dimethacrylate, trimethylolpropane trimethacrylate, tetraethyleneglycol diacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate (PETRA). The vol/vol proportion of the different co-monomers in each copolymer formulation was systematically varied, and the effect of each composition on the lasing properties of PM567 was evaluated. The laser samples were transversely pumped at 534 nm with 5.5 mJ/pulse from a frequency doubled Q-switched Nd:KGW laser. Lasing efficiencies of up 26% and good stability with a drop of the initial laser output of 30% after 100 000 pump pulses at 5 Hz in P(MMA:PETRA 95:5) were demonstrated. © 2001 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 6429-6435 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The b˜ 1B1→a˜ 1A1 emission spectrum of the CH2 radical has been studied in the 13 330–18 180 cm−1 region. Methylene (a˜ 1A1) is produced by photolysis of ketene at 308 nm and excited to single rovibrational levels of the b˜ 1B1 state by a tunable pulsed dye laser. The emission from the b˜ 1B1 state is spectrally dispersed with a resolution of 0.25 A(ring). Term values and transitions are reported for new levels of the b˜ 1B1(0,v2,0) (v2=14 and 15) and a˜ 1A1(0,0,0) states with J≥6 and 0≤Ka≤6. Unusually intense ΔKa=3 transitions and several ΔKa=5 transitions are observed. Analysis of the emission spectra gives the relative intensities of transitions from a selected rovibrational level in the upper b˜ 1B1 state to rovibrational levels in the a˜ 1A1 state. These relative intensities together with the fluorescence lifetimes of the b˜ 1B1 levels determine the absolute Einstein emission coefficients for rovibronic transitions in the visible spectrum of methylene. These data permit accurate measurement of rovibrational state populations for CH2(a˜ 1A1) by laser-induced fluorescence spectroscopy.
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