Mean Lifetime Values Research Articles

B - 101 Associations between Oxygen Saturation and Neurocognitive Performance in Sickle Cell Disease

Abstract Objective Patients with sickle cell disease (SCD) are at risk for neuropsychological deficits. Studies have documented that peripheral oxygen saturation is associated with neurocognitive performance, but the results are inconsistent. Our objective was to examine the associations between oxygen saturation and neurocognitive performance in SCD using several different measurement techniques. Methods A lifetime cohort study of 413 patients ranging from 8–25 years of age (Mean = 14.18, Standard Deviation = 4.81) diagnosed with SCD (60% HbSS) received a neuropsychological evaluation including measures of intelligence, processing speed, and working memory. Analyses were conducted separately based on SCD genotype (HbSS/Sβ0 vs. HbSC/SB+). Oxygen saturation values were examined as predictors of neurocognitive performance based on 1) mean lifetime value, 2) lifetime standard deviation, 3) most recent value (within 3 months from neuropsychological assessment), and 4) change over time. Measurement types were entered into separate multivariable models covarying for age, sex, socioeconomic status and hydroxyurea usage. Results Among patients diagnosed with HbSS/Sβ0genotypes, the lifetime standard deviation in oxygen saturation was associated with working memory (pFDR = 0.004) and the change over time in oxygen saturation was associated with processing speed (pFDR <0.001). There were no associations between oxygen saturation and neurocognitive performance among patients with the SC/SB+ genotypes. Conclusions Associations between oxygen saturation and neurocognitive performance in SCD differ based on when the values are collected and how they are analyzed. Our analyses suggest that the change over time and variability in oxygen saturation is most predictive of neurocognitive performance.

The positron and mechanical parameters of a cold-worked aluminum alloy (3004) Using PALT, PADBT and HV**

Abstract In the present work, the influence of plastic deformation on the properties of a 3004 Al-alloy was studied with different techniques. Crystallite size, dislocation density, defect density, micro-strain, and stored dislocation energy are presented and compared for different three techniques. Methodology Many techniques for detecting defects have been developed, such as the positron annihilation lifetime technique (PALT), the positron annihilation Doppler broadening technique (PADBT), and the Vickers hardness test (HV). Implications The positron mean lifetime value of a non-deformed sample is 173±4.8 ps, which increases until the thickness reduction reaches a 10% deformation then saturated at saturation trapping of the positron in defect states with a mean of 221±5 ps. At an S-parameter of 0.3709±0.0031, a W-parameter of 0.5885±0.0057 was obtained at zero deformation: this decreases until saturation at 10% deformation. Findings A good correlation between the three techniques is observed for mean crystallite size. A good correlation was also noted between PALT and PADBT from 0 to 10% thickness reduction. HV has good correlations with PALT and PADBT from 0 to 6% thickness reduction: then a clear difference was found from 6 to 15% thickness reduction. Originality such results confirm the fact that the used technique can effects on the obtained results in some limitations.

Estimation of the stored energy of dislocation for plastically deformed 6082 heat treatable Al-Alloy

This work describes cold work effect on the positron annihilation parameters, which are used in determination of the stored dislocation energy of the investigated 6082 Al-alloy samples. The investigated samples were homogenized for 6 h at 723 K then annealed at room temperature and finally plastically deformed up to 23 % degree of deformation. The annihilation parameters of the alloys under investigation were determined using the trapping model after fitting with the experimental measured data of the positron annihilation lifetime. 12% thickness reduction was found to be the start of saturation trapping region of positron in defect states at which an annihilation lifetime value of about 209±4 ps is obtained.A trapping efficiency of 6×10-7 cm3s-1 gives the best fit of the experimental measurements with the theoretical mean lifetime values obtained using the trapping model. The stored dislocation energy can be determined from the data of the positron annihilation lifetime due its ability to determine the density dislocation during plastic deformation. An increase in the strain (degree of deformation) creates comparable increase in both defect and dislocation densities, hence an increase in the measured stored dislocation energy. Maximum stored dislocation energy of about 29.5 KJ/m3 was obtained at the region of saturation of dislocation.

Comparative techniques to investigate plastically deformed 5754 Al-alloy

Cold work (compression) is an important method that produces dislocations mainly used to improve the mechanical properties of Al-alloys. The effect of deformation on 5754 Al-alloy was investigated by Positron Annihilation Lifetime Spectroscopy (PALS), Vickers micro-hardness (HV) and X-ray diffraction (XRD) techniques. The observation of results obtained by these techniques as a function of degree of deformation showed approximately the same behavior. Mean lifetime and Vickers micro-hardness values changed from 168.0 ± 7.0 ps and 32.0 ± 1.5 Hv, respectively, for the annealed (undeformed) sample to be 214.0 ± 7.0 ps and 43.0 ± 1.5 Hv, respectively, for saturated dislocation samples. Both PALS and HV results seems to be approximately constant above 8.0% degree of deformation which is the start of the saturated dislocation region. 10% degree of deformation is considered to be a threshold point or preferred orientation point obtained from XRD measurements after which saturation of dislocation is also obtained. Due to the variation in the interatomic spacing caused by plastic deformation, a significant increase in the peak broadening and line intensities of the XRD reflections is obtained.

Europium and potassium co-doped strontium metaborate single crystals grown by the Czochralski method

Strontium metaborate (SrB2O4) is a suitable material for use as a matrix for luminescent dopant ions. Similarity of ionic radii of strontium and divalent europium makes it an excellent host for Eu dopant. This paper reports on the Czochralski growth and spectroscopic study of SrB2O4 single crystals doped with europium and co-doped with europium and potassium. Based on recorded luminescence spectra it was found that both Eu3+ and Eu2+ ions occur in this host. Trivalent europium ions give rise to a narrow-band long-lived red luminescence that is not affected by incorporation of potassium ions. Divalent europium ions emit a UV–blue luminescence, consisting of a large spectral band centered at ca 430nm. In the absence of potassium ions the decay of this luminescence deviates slightly from a single exponential time dependence with a mean lifetime value of 2.0ns. In potassium-co-doped sample a strong deviation from a single exponential decay was observed for longer stages of decay, beginning at ca 2.5ns. This phenomenon was attributed to dissimilarity of relaxation rates of a fraction of europium ions distributed in different lattice sites that are distorted by the presence of big potassium ions. By co-doping the host with alkali ions one can influence the oxidation state of europium ions thereby enhancing the emission of trivalent europium ions. It was concluded that the material under study is a promising phosphor for visible light emission applications.

Nuclear lifetime measurements from data with independently varying observation times

A method is presented for obtaining ground-state and isomeric lifetimes from storage-ring data. The method published by Schmidt et al . is extended to the problems and solutions associated with applying their method to storage-ring data. These developed procedures are applied to real experimental data for 193 Re, and a mean-lifetime value of 37-7 +9 s is obtained. This is consistent with a previous measurement.

Ortho-para spin conversion of Ps by paramagnetic O2 dissolved in organic compounds

Abstract The o-Ps mean lifetime value in liquids decreases in the presence of the paramagnetic oxygen molecules via the ortho-para conversion process. This effect was observed for several organic samples composed of carbon and hydrogen atoms differing in the arrangement of atoms forming the molecule, e.g. n-alkanes, alcohols, branched isomer of alkane, cycloalkane. The usually observed tendency of the o-Ps lifetime value to be an increasing function of temperature (in the case of measurements performed in vacuum) changes to a decreasing one in the presence of O2 dissolved in the sample. The difference between the o-Ps lifetimes measured in samples in vacuum and in the presence of O2 increases with the distance from the melting point. The ortho-para constant rate λconv was estimated to be ~130 μs−1 at 300 K for three compounds investigated.

Dose estimation, kinetics and dating of fossil marine mollusc shells from northwestern part of Turkey

Electron spin resonance (ESR) spectroscopy was used to determine the geological formation age of fossil mollusc shells taken from marine terrace deposits (İkizlerçeşme-Çanakkale) in northwestern part of Turkey. This work reports the first results obtained by the ESR technique on shells collected from this region. In the ESR spectra of the natural and γ-irradiated shell samples, two different signals attributed to orthorombic (gxx=2.0030, gzz=2.0015, gyy=1.9980) and isotropic (g=2.0006) CO2− ion radicals were overlaped (Signal C). Annealing and kinetic experiments suggest the possibility of using the ESR signal at g=2.0015 (C signal) for the estimation of accumulated geological doses. The ESR signal growth curve on additional gamma irradiation has been best fitted by a combination of two single exponential saturation functions. This may support the existence of at least two components of the g=2.0015 ESR dating signal. Based on this model, the accumulated dose of the samples was determined as 110±11Gy. Also the isothermal decay curves of the ESR dating signal could be best described by the combination of two first order decay functions. Activation energy and meanlifetime values at 15°C of the two components were calculated as E1=1.4±0.1eV, E2=1.1±0.1eV, τ1=7.2×106 years and τ2=3.3×103 years, respectively. Uranium content of the studied shells was found to be high according to their chemical analysis. This may point out that the marine shell has received uranium from outside particularly in carbonate sediment. Therefore, the ESR age of the samples was also calculated using Early Uptake (EU), Linear Uptake (LU) and Combined Uptake (CU) models and results were discussed.

Fluorescence Lifetime Imaging of Membrane Lipid Order with a Ratiometric Fluorescent Probe

To monitor the lateral segregation of lipids into liquid-ordered (Lo) and -disordered (Ld) phases in lipid membranes, environment-sensitive dyes that partition in both phases but stain them differently have been developed. Of particular interest is the dual-color F2N12S probe, which can discriminate the two phases through the ratio of its two emission bands. These bands are associated with the normal (N∗) and tautomer (T∗) excited-state species that result from an excited-state intramolecular proton transfer. In this work, we investigated the potency of the time-resolved fluorescence parameters of F2N12S to discriminate lipid phases in model and cell membranes. Both the long and mean lifetime values of the T∗ form of F2N12S were found to differ by twofold between Ld and Lo phases as a result of the restriction in the relative motions of the two aromatic moieties of F2N12S imposed by the highly packed Lo phase. This differed from the changes in the ratio of the two emission bands between the two phases, which mainly resulted from the decreased hydration of the N∗ form in the Lo phase. Importantly, the strong difference in lifetimes between the two phases was preserved when cholesterol was added to the Ld phase. The two phases could be imaged with high contrast by fluorescence lifetime imaging microscopy (FLIM) on giant unilamellar vesicles. FLIM images of F2N12S-labeled live HeLa cells confirmed that the plasma membrane was mainly in the Lo-like phase. Furthermore, the two phases were found to be homogeneously distributed all over the plasma membrane, indicating that they are highly mixed at the spatiotemporal resolution of the FLIM setup. Finally, FLIM could also be used to sensitively monitor the change in lipid phase upon cholesterol depletion and apoptosis.

Variational Photocarrier Radiometry Reconstruction of Exciton Lifetime Spectra for a Coupled PbS Colloidal Quantum Dot Thin Film Under Combined AC and DC Laser Excitation

Colloidal quantum dots (CQDs) have attracted significant interest for applications in electronic and optoelectronic devices such as photodetectors, light emitting diodes, and solar cells. However, a poor understanding of charge transport in these nanocrystalline films hinders their practical applications. The photocarrier radiometry (PCR) technique, a frequency-domain photoluminescence method spectrally gated for radiative recombination photon emissions and exclusion of thermal infrared photons, has been applied to a coupled PbS CQD thin film with inter-dot spacing of 0.5 nm to 1 nm for the analysis of charge transport properties. As the nanoparticle bandgap depends on the size of the quantum dots, polydispersity of the CQD thin film causes bandgap variability leading to photoexcited carrier (exciton) decay lifetime broadening and temperature dependence. The carrier transport mechanisms of QDs are quite different from bulk semiconductors, so the conventional carrier-diffusion wave-based PCR theory was modified into a non-diffusive limit model. A developed variational discrete lifetime reconstruction approach was used to analyze PCR frequency scans under two optical excitation modes: a modulated laser source without, and with, an additional continuous laser source. Using this model, the CQD mean lifetime values were found and variational discrete lifetime spectra were reconstructed.

Site-specific fluorescence dynamics in an RNA 'thermometer' reveals the role of ribosome binding in its temperature-sensitive switch function.

RNA thermometers control the translation of several heat shock and virulence genes by their temperature-sensitive structural transitions. Changes in the structure and dynamics of MiniROSE RNA, which regulates translation in the temperature range of 20–45°C, were studied by site specifically replacing seven adenine residues with the fluorescent analog, 2-aminopurine (2-AP), one at a time. Dynamic fluorescence observables of 2-AP-labeled RNAs were compared in their free versus ribosome-bound states for the first time. Noticeably, position dependence of fluorescence observables, which was prominent at 20°C, was persistent even at 45ºC, suggesting the persistence of structural integrity up to 45ºC. Interestingly, position-dependent dispersion of fluorescence lifetime and quenching constant at 45°C was ablated in ribosome-bound state, when compared to those at 20°C, underscoring loss of structural integrity at 45°C, in ribosome-bound RNA. Significant increase in the value of mean lifetime for 2-AP corresponding to Shine–Dalgarno sequences, when the temperature was raised from 20 to 45°C, to values seen in the presence of urea at 45°C was a strong indicator of melting of the 3D structure of MiniROSE RNA at 45°C, only when it was ribosome bound. Taken all together, we propose a model where we invoke that ribosome binding of the RNA thermometer critically regulates temperature sensing functions in MiniROSE RNA.

Specification of the State's Lifetime in the Devs Formalism by Fuzzy Controller

This paper aims to develop a new approach to assess the duration of state in the DEVS formalism by fuzzy controller. The idea is to define a set of fuzzy rules obtained from observers or expert knowledge and to specify a fuzzy model which computes this duration, this latter is fed into the simulator to specify the new value in the model. In conventional model, each state is defined by a mean lifetime value whereas our method, calculates for each state the new lifetime according to inputs values. A wildfire case study is presented at the end of the paper. It is a challenging task due to its complex behavior, dynamical weather condition, and various variables involved. A global specification of the fuzzy controller and the forest fire model are presented in the DEVS formalism and comparison between conventional and fuzzy method is illustrated.

Isochronal annealing of a deformed Fe-7.5 mass.% Si-steel

Abstract FeSi samples with 7.5 mass.% Si were cold deformed with a thickness reduction of 16% and isochronally annealed for one hour at different temperatures. Their microstructure was characterised using positron annihilation lifetime spectroscopy and electron backscatter diffraction. Positron annihilation mean lifetime values (τmean) decreased slightly with the increase in annealing temperature (20 to 600°C), a process related to recovery. In addition, τmean decreased significantly in the 700–900°C temperature range. The measured value of τmean is 106 ps, which is similar to the pure undeformed Fe after annealing at 900°C. Thus, the material is virtually free of defects at 900°C. Microscopy and diffraction studies showed a high amount of shear bands for the deformed sample. In the temperature range of 20–600°C, no recrystallisation was observed. According to the electron backscatter diffraction data, the recrystallisation starts after 700°C, and it is completed at 900°C.

Atomic fraction around defects associated with nanoparticles in AlCuMg alloys

A positron annihilation spectroscopy analysis method to obtain a quantitative determination of the chemical composition around defects inside nanoparticles is presented here. This methodology is applied to AlCuMg alloys to study the rapid hardening phenomena associated with solute-vacancy aggregation. Coincidence Doppler Broadening (CDB) and lifetime spectroscopy measurements of reference samples of pure elements with and without defects were analyzed to give quantitative information of the average chemical environment around vacancies, i.e. the atomic fraction of the first neighbors of these defects, in the alloys studied. The accuracy and reproducibility of the methodology is confirmed not only by good fits to the experimental data but, in most cases, by the consistency between the mean lifetime values predicted, using the CDB estimation, and the mean lifetime values independently measured. Discrepancies in the methodology are expected when there is poor CDB contrast between elements, i.e. having similar electronic structure (for example, Al and Mg). The criterion for establishing the statistical accuracy of the separation of elements in these special cases is discussed. The methodology can be applied not only to study homogeneous materials as metallic alloys, but also to study the depth profile in thin films.

Dynamics of tRNAtyr Probed with Long-Lifetime Metal-Ligand Complexes

The metal-ligand complexes, [Ru(bpy)(2)(dppz)](2+) (bpy = 2,2'-bipyridine, dppz = dipyrido[3,2-a:2',3'-c]phenazine) (RuBD) and [Ru(phen)(2)(dppz)](2+) (phen = 1,10-phenanthroline) (RuPD), display favorable photophysical properties including long lifetime, polarized emission, and very little background fluorescence. To check if RuBD and RuPD reflect the overall rotational mobility of small nucleic acid, we measured the intensity and anisotropy decays of RuBD and RuPD when intercalated into tRNA(tyr) using pBC SK(+) phagemid as a control. We used frequency-domain fluorometry with a blue light-emitting diode (LED) as the modulated light source. We observed shorter lifetimes for tRNA(tyr) than those for the pBC SK(+) phagemid for both probes, however, RuPD showed much larger decrease in the mean lifetime values (64%). The slow rotational correlation time of RuBD (31.3ns) and the fast rotational correlation time of RuPD (26.0ns) reflected the overall rotational mobility of tRNA(tyr). In addition, the steady-state anisotropy and time-resolved anisotropy decay data showed a clear difference between tRNA(tyr) and pBC SK(+) phagemid. This suggests the possibility of a homogeneous assay for identifying target nucleic acids and/or nucleic acid binding proteins.

Positron Annihilation Lifetime Spectroscopy in the analysis of microstructural changes of Y-TZP ceramics

Positron Annihilation Lifetime Spectroscopy (PALS) technique was used for microstructural characterisation of Y-TZP ceramics. Spectroscopic measurements were carried out on ceramic surfaces subjected to tribological tests. Positron annihilation mean lifetime values, measured both on the unworn and worn surfaces, showed a different behaviour when different sliding velocities were used. For samples tested at 0.3 and 0.7 m/s, the decrease of values of positron mean lifetime measured on the worn surfaces, compared with the measurements of the unworn surfaces, was related to the increased positron trapping in the grain-boundary-related space-charge region, due to defect equilibrium changes with grain size reduction. For samples tested at 1.0 m/s, the higher mean lifetime values, found on the worn surfaces, was ascribed to the increase in zirconia monoclinic phase fraction present on the worn scars.

Testing ETE model, temperature dependences of PALS data

AbstractThree porous glasses produced by sol‐gel method were investigated using Positron annihilation lifetime spectroscopy (PALS) method. The theoretical curves calculated from the pick‐off annihilation model for cylindrical and spherical free volumes were compared to the results of PALS measurements done in the temperature range from 100 to 500 K. The o‐Ps mean lifetime values in the pores found in the experiment change with temperature in the glasses containing pores of R < 1.5 nm in the range up to 40 ns, while the model predicts these changes less then 10 ns. The meaningful discrepancy between experimental data and model predictions was found at low temperatures. The discrepancy diminishes with increasing pore sizes. In the glass containing the largest pores, R ∼ 2 nm, experimental values of o‐Ps lifetime agree well with model predictions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Positron Lifetime in Deformed AlSi10.9Mg0.17Sr0.06 Alloys

Positron annihilation lifetime spectroscopy (PALS) is one of the nuclear techniques used in material science. (PALT) measurements are used to study the behaviour of the defect concentration in a set of AlSi10.9Mg0.17Sr0.06 alloys. It has been shown that positrons can become trapped at imperfect locations in solids, and that their mean lifetime can be influenced by changes in the concentration of such defects. No changes have been observed in the mean lifetime values following saturation of the defect concentration. The mean lifetime and trapping rates were studied for samples deformed up to 34.9 %. The concentrations of defects range vary from 5.194x1015 to 1.934x1018 cm-3 for thickness reductions of 2.2 to 34.9 %. The range of the dislocation density varies from 1.465x 108 to 5.454x1010 cm/cm3 over the same range of deformations.

DETECTING DEFECTS IN AIRCRAFT MATERIALS BY NUCLEAR TECHNIQUE (PAS)

Positron annihilation spectroscopy (PAS) is one of the nuclear techniques used in material science. The present measurements are used to study the behavior of defect concentration in one of the most important materials — aluminum alloy — which is a 7075 alloy. It has been shown that positrons can become trapped in imperfect locations in solids and their mean lifetime can be influenced by changes in the concentration of such defects. No changes have been observed in the mean lifetime values after the saturation of defect concentration. The mean lifetime and trapping rates were studied for samples deformed up to 58.3%. The concentration of defect range varies (from 1015 to 1018 cm-3) at the thickness reduction, (from 2.3 to 58.3%). The range of the dislocation density varies (from 108 to 1011 cm/cm3).

DETECTING DEFECTS IN AIRCRAFT MATERIALS BY NUCLEAR TECHNIQUE (PAS)

Positron annihilation spectroscopy (PAS) is one of the nuclear techniques used in material science. The present measurements are used to study the behavior of defect concentration in one of the most important materials aluminum alloys which is the 7075 alloy. It has been shown that positrons can become trapped at imperfect locations in solids and their mean lifetime can be influenced by changes in the concentration of such defects. No changes have been observed in the mean lifetime values after the saturation of defect concentration. The mean lifetime and trapping rates are studied for samples deformed up to 58.3%. The concentration of defect range vary from 1015 to 1018 cm -3 at the thickness reduction from 2.3 to 58.3%. The dislocation density varies from 108 to 1011 cm/cm 3.