Observed Decay Curves Research Articles

Superhyperfine induced photon-echo collapse of erbium in Y2SiO5

We investigate the decoherence of Er$^{3+}$ in Y$_2$SiO$_5$ at low magnetic fields using the photon-echo technique. We reproduce accurately a variety of the decay curves with a unique coherence time by considering the so-called superhyperfine modulation induced by a large number of neighbouring spins. There is no need to invoke any characteristic time of the spin fluctuations to reproduce very different decay curves. The number of involved nuclei increases when the magnetic is lowered. The experiment is compared with a model associating 100 surrounding ions with their exact positions in the crystal frame. We also derive an approximate spherical model (angular averaging) to interpret the main feature the observed decay curves close to zero-field.

Closing the ultrafine particle number concentration budget at road-to-ambient scale: Implications for particle dynamics

Freshly emitted vehicle exhaust particles are diluted quickly as they mix into ambient air, but the contribution of evaporation, coagulation, and/or nucleation of new particles to the number concentration has been the subject of some debate. We analyzed one-second time resolution size distribution data from an early morning field campaign, data collected at a time at which dilution has a smaller (but still dominant; ∼70−80%) impact on particle concentrations. Because the plume is diluted over an hour, and a distance of 1500 m, we can constrain the processes with higher accuracy. We find that concentrations in the smaller size bins (5.6–23.7 nm) peak further downwind than the reference particles (42.1–562 nm), and decay significantly faster than larger particles particularly in the area 100−400 m downwind. Comparisons of the cumulative contributions of van der Waals enhanced coagulation, dry deposition, and dilution and the observed decay curves, imply that for up to the first 50–100 m there is nucleation and/or growth of particles smaller than 5.6 nm. In contrast, in the ∼100–400 m region, some of the smaller particles evaporate. In the further downwind areas (>400 m) the particles all appear to decay at rates consistent with the sum of dilution, coagulation, and deposition. We also find that a dry deposition parameterization at the low end of those available in the literature is most consistent with the observational data.© 2016 American Association for Aerosol Research

Crustal structure in and around the Onikobe geothermal area, northeastern Honshu, Japan, inferred from the spatial variation of coda decay

The Onikobe area is an active geothermal area situated in the Ou backbone range of northeastern Honshu, Japan. It is home to calderas from the Tertiary to Quaternary eras and active volcanoes. A systematic spatial variation of Qc has been found in this area: Qc values are lower at stations in and around calderas than at other stations. The amplitude of coda waves with high Qcs decreases more slowly after a lapse time of around 7–10s than that with low Qcs. In the present study, to determine causes for these coda decay variations, coda envelopes were synthesized in a structure model in which high attenuation zones existed beneath the Onikobe and Sanzugawa calderas and where scattering coefficients were higher in the lower crust than in the upper crust. Using hypocenters shallower than 10km, envelopes were calculated for 256 station-hypocenter pairs with epicentral distances of less than 10km. It was assumed that the coda waves were composed of S–S scattered waves, and that the scattering was single and isotropic. The observed features of the Qc distribution were reproduced in the synthesis, and synthesized envelopes were found to mostly coincide with observed decay curves. The top of high attenuation zones was thus estimated as being deeper than 7.5km. The structure assumed for the synthesis was consistent with that of previous studies. We consider that the structure model used was appropriate, and that high attenuation zones beneath calderas and the reflective lower crust caused the spatial variation of the Qc and decay curves in the Onikobe area. We also consider that studies using coda decay would be beneficial in detecting high attenuation zones and the reflective lower crust.

Local site symmetry of Sm3+ in sol–gel derived α′-Sr2SiO4: Probed by emission and fluorescence lifetime spectroscopy

Trivalent samarium-doped strontium silicate (Sr2SiO4) phosphors were prepared by sol–gel synthesis using tetra ethyl orthosilicate (TEOS) as precursor. The synthesis temperature could be brought down to 600°C for the formation of a single phase sample. The emission and excitation spectra, and decay curves were employed to study the luminescence properties. The calcined powders of the Sm3+ ions doped in the Sr2SiO4 emit reddish orange light. In our present study, the 4G5/2→6H5/2 (MD) transition of Sm3+ ions is less intense than 4G5/2→6H9/2 (ED) transition. This indicates that Sm3+ ions preferentially occupy asymmetric site in α-Sr2SiO4. Fluorescence life time measurement has shown monoexponential behavior for Sm3+ in strontium silicate with lifetime value of 2.23ms. Based on lifetime and emission spectra, it can be inferred that Sm3+ occupies 9-coordinated Sr2+ site in strontium silicate. Based on stark splitting pattern it was inferred that site symmetry around Sm3+ is C3v which further justifies it׳s occupancy in 9-coordinated sites. It was observed that, the emission intensity of Sm3+ increases with the increase in concentration initially, reaching maxima at 1.0mol % and then decreases with the increasing concentration due to concentration quenching. At higher concentrations (x>0.01), however, the observed decay curves were bi-exponential.

Bentonite pore distribution based on SAXS, chloride exclusion and NMR studies

AbstractWater-saturated bentonite is planned to be used in many countries as an important barrier component in high-level nuclear waste (HLW) repositories. Knowledge about the microstructure of the bentonite and the distribution of water between interlayer (IL) and non-interlayer (non-IL) pores is important for modelling of long-term processes. In this work the microstructure of water-saturated samples prepared from MX-80 bentonite was studied with nuclear magnetic resonance (NMR) and small-angle X-ray scattering spectroscopy (SAXS) coupled with chloride exclusion modelling. The sample dry densities ranged between 0.7 and 1.6 g/cm3. The NMR technique was used to get information about the relative amounts of different water types. Water in smaller volume domains has a shorter relaxation time than that in larger domains due to the average closer proximity of the water to the paramagnetic Fe at the layer surfaces. The results were obtained using1H NMRT1ρrelaxation time measurements with the short inter-pulse CPMG method. The interpretation of the NMR results was made by fitting a sum of discrete exponentials to the observed decay curves. The SAXS measurement on bentonite samples was used to get information about the size distribution of the IL distance of montmorillonite. The chloride porosity measurements and Donnan exclusion calculations were used together with the SAXS results to evaluate the bentonite microstructure. In the model, the montmorillonite layers were organized in stacks having IL water between the layers and non-IL water between the stacks. In the modelling, the number of layers in the stacks was used as fitting parameters which determined the IL and non-IL surface areas. The fitting parameters were adjusted so that the modelled chloride concentration was equal to the measured one. The NMR studies and SAXS studies coupled with the Cl porosity measurements provided very similar pictures of how the porewater is divided in two phases in bentonite.

Use of principal component images for classification of the EM response of unexploded ordnance

The location and identification of unexploded ordnance (UXO) is a major challenge for environmental rehabilitation of former military firing ranges and bombing target areas. EM methods are in widespread use for the location of metal objects, however the presence of large quantities of scrap metal from successful detonation of munitions makes discrimination between munitions and scrap and munitions of various sizes a necessity in order for efficient location, digging and removal of UXOs to proceed. Several recent papers show that detailed three-component EM measurements followed by inversion to dipole moments of an EM target is effective in characterising a target, however such techniques require precise data, usually from stationary data acquisition. EM data acquired from a moving ground platform for UXO detection is typically high in motion-induced noise which limits the usefulness of decay-curve analysis in target characterization. We use a data set from the Australian Air Force Newholme UXO Test Range, Armidale, NSW, and show that a) images of time-window data are unsuccessful in discriminating between different types of munitions, b) adaptive decay index methods are ineffective due to high noise levels on the observed decay curves, and c) principal-component transforms of the data are successful in differentiating between different types of munitions. The method provides a tool for initial classification and prioritization of anomalies from a surveyed area, thus facilitating preparation of an efficient program of follow-up surveys and site clean-up.

Atomic lifetime measurements on forbidden transitions of Al-, Si-, P- and S-like ions at a heavy-ion storage ring

Lifetimes of 3s23pk ground configuration levels of Al-, Si-, P- and S-like ions of Fe, Co and Ni have been measured at a heavy-ion storage ring. Some of the observed decay curves show strong evidence of cascade repopulation from specific 3d levels that feature lifetimes in the same multi-millisecond range as the levels of the ground configuration. We identify the foil-stripping process in the ion production as the cause of the cascade level population and assess the importance of specific cascades for the measurement technique.

Fluorescence Fluctuation Spectroscopy in the Presence of Immobile Fluorophores

Fluorescence contributions from immobile sources present a challenge for fluorescence fluctuation spectroscopy (FFS) because the absence of signal fluctuations from stationary fluorophores leads to a biased analysis. This is especially of concern for cellular FFS studies on proteins that interact with immobile structures. Here we present a method that correctly analyzes FFS experiments in the presence of immobile sources by exploiting selective photobleaching of immobile fluorophores. The fluorescence decay due to photobleaching of the immobile species is modeled taking into account the nonuniform illumination volume. The experimentally observed decay curve serves to separate the mobile and immobile fluorescence contribution, which is used to calculate the molecular brightness from the FFS data. We experimentally verify this approach in vitro using the fluorescent protein EGFP as our immobilized species and a diffusing dye of a different color as the mobile one. For this special case, we also use an alternative method of determining the brightness by spectrally resolving the two species. By conducting a dilution study, we show that the correct parameters are obtained using either technique for a wide range of mobile fractions. To demonstrate the application of our technique in living cells, we perform experiments using the histone core protein H2B fused with EGFP expressed in COS-1 cells. We successfully recovered the brightness of the mobile fraction of H2B-EGFP.

Life-time resolved emission spectra in CdI 2 crystals

The emission spectrum of CdI 2 is composed of ultraviolet (UV), green (G) and yellow (Y and Y′) bands peaking at 3.38, 2.50, 2.16 and 2.25 eV, respectively. In order to determine the initial states of the Y- and G-luminescence, decay curves have been measured at 6 and 80 K by varying emission energy. The observed decay curves are composed of two or three exponential components. These decay components were named τ 1, τ 2, τ 3, τ 3′ and τ 4. The emission spectrum for each decay component, i.e., the life-time resolved emission spectrum, was constructed from the observed decay curves. At 6 K, three bands at 2.12, 2.49 and 2.64 eV are obtained for τ 1, τ 2 and τ 3 components, respectively. At 80 K, a dominant band for the τ 4 component and a weak band for the τ 3′ component appear on the same energy position at 2.25 eV. The origin of each emission band in the life-time resolved emission spectra will be briefly discussed.

Time and temperature dependence of the emissions from the quantum-cutting phosphor [formula omitted

The Gd–Eu couple is well known for efficient conversion of absorbed high-energy photons into two visible photons (quantum cutting). For this couple, a model describing the quantum-cutting mechanism has been proposed by Wegh et al. [J. Lumin. 82 (1999) 93]. This model is mainly supported by emission spectra, while the kinetics of the energy-transfer processes involved in quantum cutting have hardly been investigated. The present paper reports time and temperature dependent studies of the spectroscopic properties of LiGdF 4 : Eu 3 + 0.5%. The experimentally observed decay curves at room temperature of the Eu 3 + 5D 0, 5D 1 and Gd 3 + 6P 7/2 emission can be explained by a parameter model based on the kinetics of the mechanism. The temperature-dependent study shows a change in the energy-transfer kinetics that is consistent with the absence of quantum cutting at low temperatures ( T < 50 K ) .

Quantitative Analysis of Backbone Dynamics in a Crystalline Protein from Nitrogen-15 Spin−Lattice Relaxation

A detailed analysis of nitrogen-15 longitudinal relaxation times in microcrystalline proteins is presented. A theoretical model to quantitatively interpret relaxation times is developed in terms of motional amplitude and characteristic time scale. Different averaging schemes are examined in order to propose an analysis of relaxation curves that takes into account the specificity of MAS experiments. In particular, it is shown that magic angle spinning averages the relaxation rate experienced by a single spin over one rotor period, resulting in individual relaxation curves that are dependent on the orientation of their corresponding carousel with respect to the rotor axis. Powder averaging thus leads to a nonexponential behavior in the observed decay curves. We extract dynamic information from experimental decay curves, using a diffusion in a cone model. We apply this study to the analysis of spin-lattice relaxation rates of the microcrystalline protein Crh at two different fields and determine differential dynamic parameters for several residues in the protein.

Life‐time resolved emission spectra in CdCl 2 crystals

The emission spectrum of CdCl2 is composed of ultraviolet (UV) and yellow (Y) bands peaking at 3.70 and 2.30 eV, respectively. In order to determine the initial states of the Y-luminescence, decay curves of the Y-emission were measured at 8K by varying emission energy in the range from 1.64 eV to 3.13 eV. The observed decay curves are composed of two or three exponential components. The values of lifetime for them were 900, 460 and 60 µs. The emission spectrum for each decay component, i.e., life-time resolved emission spectrum, was analyzed by the observed decay curves. The emission spectrum for the component of 460 µs lifetime exhibits a dominant band at 2.30 eV and a satellite band at 3.03 eV. The emission spectrum for the component of 60 µs lifetime is reproduced by the three Gaussian bands peaking at 2.21, 2.65 and 2.87 eV. For the component of 900 µs lifetime, only a single band appears at 1.73 eV. The origin of the emission bands in life-time resolved emission spectra is briefly discussed, and the initial states of Y-luminescence are explained by the excited states of a [Cd2+Cl–6] 4– complex molecular ion. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Life-time resolved emission spectra in CdBr 2 crystals

Decay curves of the Y-emission were measured at 60, 100 and 140 K by varying emission energy in the range of the Y-emission. The observed decay curves were decomposed into three or four exponential decay components. These decay components were named τ 1, τ 2, τ 4 and τ 5. The emission spectrum for each decay component, i.e., life-time resolved emission spectrum, was obtained by analyzing the observed decay curves. At 60 K, three bands at 1.95, 2.24 and 2.47 eV are obtained for the τ 5, τ 4 and τ 1 components, respectively. For the τ 2 component, sharp peaks appear around 2.30–2.50 eV. At 100 K, a dominant band of the τ 4 component is seen at 2.25 eV. In the low-energy side, a weak band of the τ 5 component is located at 1.95 eV. At 140 K, only a single band of the τ 4 component is observed at 2.27 eV. The origin of emission bands in life-time resolved emission spectra is discussed.

Intra- and Intermicellar Triplet−Triplet Annihilation of Pyrenetetrasulfonate in an AOT Reverse Micellar Solution: Relation to the Electric Percolation Transition

Decay behaviors of triplets were investigated as a function of temperature in ternary (water/AOT/oil) and quaternary (water/AOT/cosurfactant/oil) reverse micellar solutions. The triplet species generated by the laser irradiation of tetrasodium pyrenetetrasulfonate dissolved in a reverse micelle were detected by monitoring the triplet-triplet absorption at 430 nm. The observed decay curves were analyzed with the kinetic model combining the intermicellar triplet-triplet annihilation (TTA) with the intramicellar TTA. The kinetic model for the intermicellar TTA process was proposed on the basis of the equilibrium between the monomer and dimer micelles. The obtained kinetic parameters and thermodynamic quantities are discussed in relation to electric percolation phenomena in these micellar systems. A fraction of the dimer micelles was found to be almost constant (0.27 ′ 0.03) at the percolation temperature for all of the reverse micellar systems that were investigated. Furthermore, an average number of triplets per micelle and the Gibbs free energy change for dimer micelle formation seem to be closely related to the percolation threshold. These results suggest that the laser-induced transient absorption spectroscopy of a probe is a useful method for studying dynamic behavior in micellar systems.

A Study of Dynamic Adsorption Characteristics of Chlorinated Organic Solvents onto the Activated Carbon Particles: Chloroform and/or 1,2-Dichloropropane-Activated Carbon Systems

To elucidate the kinetic characteristics of the adsorption of organic solvents dissolved in water onto a solid adsorbent, the authors proposed an elaborated experimental scheme where the adsorptive components can be batchwisely taken up from the aqueous medium, being well stirred in a vessel without dead space. The present study deals with chloroform (CH)–water and/or 1,2-dichloropropane (DCP)–water systems.It can be concluded from the observed isotherms that DCP can adsorb more strongly than the other over the whole concentration range examined.On the basis of the measured transient concentration decay curves and the mathematically simulated ones for single component systems, it can be concluded that the predominant mass transfer resistance would be confined within the solid phase, and the simulated effective diffusion coefficients for CH and DCP increased linearly with an increasing adsorption amount for each component, which does not contradict the previous results of other investigators.To predict the adsorption amount of each component in a binary mixture system, the authors employed a widely acknowledged Ideal Adsorbed Solution Model (IAS) and concluded that the model is successfully applicable to the present mixture system. Some transient decay curves were also measured for the binary systems.Incorporating the IAS model into the mass transfer governing equations, the authors simulated the observed decay curves in terms of the effective diffusion coefficients. As a result, the coefficient of DCP for the binary system is compatible with that for the single component system, while the coefficient for CH is larger than that for the single component system.

Intermolecular exchange of vibrational population in a binary liquid mixture

Using a picosecond infrared pump–probe technique, we have studied the decay of transient excess population of the CH stretch vibrational modes in binary liquid mixtures of CHBr3 and CHCl3. Analyzing the concentration dependence of the observed decay curves on the basis of a simple rate equation model gives strong evidence for an effective resonant transfer of vibrational energy between the two different types of molecules. A value of κ=[(22±5) ps]−1 is determined for the rate constant κ describing this process. This value is larger than the total relaxation rates of both neat bromoform and chloroform indicating that even there CH stretching quanta can be transferred from molecule to molecule several times before they are relaxing.

Vibrational and rotational cooling ofH3+

The vibrational relaxation of ${\mathrm{H}}_{3}^{+}$ molecules from a conventional plasma ion source is studied performing Coulomb explosion imaging on the ions extracted from a storage ring after variable times of storage. Storage for 2 s is found sufficient for radiative relaxation of the breathing excitation and the fragment velocity distribution in the breathing coordinate then agrees well with simulations based on the calculated ground-state wave function. The radiative decay of the two lowest pure breathing levels ${(1,0}^{0})$ and ${(2,0}^{0})$ is seen to be considerably faster than expected from rotationless calculations. Assuming a high rotational excitation of the ${\mathrm{H}}_{3}^{+}$ ions, as suggested already in earlier experiments, the theoretical transition probabilities of the University College London line list for ${\mathrm{H}}_{3}^{+}$ [L. Neale, S. Miller, and J. Tennyson, Astrophys. J. 464, 516 (1996)] can explain the increase of the vibrational cooling rates and reproduce the observed decay curve for the lowest breathing-excited level, confirming the absolute transition probabilities of these line tables. The observations give evidence for a quasistable population of high-lying rotational levels in the stored ion beam, relevant for the interpretation of storage ring measurements on the rate coefficients for dissociative recombination of ${\mathrm{H}}_{3}^{+}$ ions with low-energy electrons.

Formation and Decay Behaviors of Laser-Induced Transient Species from Pyrene Derivatives 2. Micellar Effects

Micellar effects were investigated on the decay behaviors of several transient species such as triplet and cation radical that were produced by laser irradiation of three pyrene derivatives (sodium pyrenesulfonate (NaPS), tetrasodium pyrenetetrasulfonate (Na4PS4), and pyrenebutyric acid (HPB)). Those compounds were solubilized in Aerosol OT (AOT) reverse micellar solutions with different molar ratios of [H2O]/[AOT](W). The W-dependent decay curves of triplets from PS44- and PS- were analyzed with the kinetic model involving both the intra- and intermicellar triplet−triplet annihilations (TTA). As a result, the triplets were found to decay through two different TTA mechanisms: T + T → T + S0 for PS44- triplet and T + T → S1 + S0 for PS- triplet, respectively. It is shown that the PS44- triplet is a useful probe for determination of the aggregation number per micelle. In the case of their cation radicals, the decay curves, in addition to the yields, were found to largely depend on W and atmospheric gases. The present results can be interpreted in terms of size and physicochemical properties of the water pool, location of the probe molecule in a micelle, and the nature of the cation radical formed. The dependence of the cation radical from PS- is consistent with the two distinct locations model in which PS- molecules are distributed into both water pool and palisade layer. On the other hand, two types of cation radicals, completely charge-separated and intramolecular charge-separated species, have been proposed to explain the observed decay curves of the cation radical from PS44- in the water pool. Both the formation and the decay behavior of the latter cation radical were found to reflect the ionic environment of the water pool.

Quantum beats in the S1 dynamics of glyoxal

Fluorescence of transition à 1Au−X̃ 1Ag of trans-glyoxal in a supersonic jet is recorded with laser excitation in the wavelength region 393–417 nm. Full rotational analysis is performed for nine bands in a region 395–410 nm. Fluorescence decays with quantum beats from several rovibrational levels in à 1Au of glyoxal are detected. As lines in Fourier-transform spectra of those decay curves split on application of an external magnetic field, this oscillatory behavior results from coherent excitation of mixed S1 and T1 states. On excitation with high energy, those lines become broadened as the lifetime of the T1 state decreases because of coupling to a dissociation continuum. An abrupt increase of linewidth in transformed spectra at 25 350 cm−1 (394.5 nm) indicates that this position corresponds to a threshold for dissociation. For excitation energy greater than 25 450 cm−1, most observed decay curves of fluorescence emission display biexponential behavior. The decay of the fast component of the biexponential curve corresponds to intersystem crossing and the slow component to decay of those eigenstates. For energies exceeding 25 550 cm−1, the slow component diminishes, to yield nearly single exponential decay, indicating that the rate of dissociation is greater than that of intersystem crossing. Results of these quantum-beat experiments imply a new dissociation pathway from the triplet surface.

Dependence of scintillation characteristics in the CsI(Tl) crystal on Tl/sup +/ concentrations under electron and alpha particles excitations

This paper reports the emission spectra, pulse heights, and decay curves of CsI(TI) crystals with a Tl/sup +/ concentration ranging from 10/sup -6/ to 10/sup -2/ mol under electron and alpha particle excitations. Larger pulse heights from the crystals with Tl/sup +/ concentration of more than 10/sup -3/ mol were observed for a higher ionization density of alpha particle excitation compared with those of electron excitation. This enhancement may be explained in terms of the higher scintillation efficiency for higher Tl/sup +/ concentration. Decay curves under electron and alpha particle excitations were compared with the decay curve under pulsed UV excitation. The observed decay curves were explained in terms of the sum of the three energy transfer processes to create excited states (Tl/sup +/)*: the prompt process, the V/sub k/ diffusion process to Tl/sup 0/, and the electron release process from Tl/sup 0/ to Tl/sup ++/. Here, Tl/sup 0/ and Tl/sup ++/ were produced through (Tl/sup +/+electron)/spl rarr/Tl/sup 0/ and [Tl/sup +/+hole (or V/sub k/)]/spl rarr/Tl/sup ++/.