Changes In Lifetime Research Articles

Association of Lifetime Earning Potential and Workforce Distribution Among Pediatric Subspecialists

Differences in lifetime earning potential between pediatric subspecialties may contribute to shortages in the subspecialty workforce. To evaluate the association between lifetime earning potential and workforce distribution and to investigate the potential role of a pediatric subspecialist-specific loan repayment program (LRP) in workforce expansion. This study was performed on publicly available mean debt and compensation data from national physician surveys from 2018 to 2019 of pediatric subspecialists in academic practice. Linear regression analysis was used to evaluate the association between lifetime earning potential and measures of workforce distribution in 2019, including distance to subspecialists, percentage of hospital referral regions with a subspecialist, and ratio of subspecialists to the regional child population as well as between lifetime earning potential in 2018 to 2019 and mean subspecialty fellowship fill rates between 2014 and 2018. The association between the change in lifetime earning potential from 2007 to 2018 and the change in workforce distribution metrics from 2003 to 2019 was also examined. The potential role of a pediatric subspecialist-specific LRP was modeled. Lifetime earning potential by subspecialty. Measures of workforce distribution and fellowship fill rates. This study included mean compensation data representing 7539 pediatric subspecialists, workforce distribution data representing 24 375 pediatric subspecialists, and fellowship fill rates representing a mean of 1344 pediatric subspecialty fellows per year. Higher lifetime earning potential was associated with shorter distance to subspecialists (-0.59 miles/$100 000 increase in lifetime earning potential; 95% CI, -1.10 to -0.09), higher percentage of hospital referral regions with a subspecialist (+1.17%/$100 000 increase in lifetime earning potential; 95% CI, 0.34-2.00), and higher ratio of subspecialists to regional child population (+0.11 subspecialists/100 000 children/$100 000 increase in lifetime earning potential; 95% CI, 0.04-0.19). The subspecialties for which lifetime earning potential increased the least between 2007 and 2018 experienced the least growth in the ratio of subspecialists to regional child population from 2003 to 2019 (+0.11 subspecialists/100 000 children/$100 000 increase in lifetime earning potential; 95% CI, 0.07-0.16). Higher lifetime earning potential was associated with higher mean fellowship fill rates (+0.96% spots filled/$100 000 increase in lifetime earning potential; 95% CI, 0.15-1.77). Implementing a pediatric subspecialist-specific LRP could increase fellowship fill rates and improve workforce distribution. Lifetime earning potential based on subspecialty may contribute to imbalances in both the current and future pediatric subspecialty workforce. Pediatric subspecialist-specific LRPs, especially for underfilled subspecialties, are potential tools for policy makers to target workforce shortages.

Single-Molecule White-Light-Emitting Starburst Donor-Acceptor Triphenylamine Derivatives and Their Application as Ratiometric Luminescent Molecular Thermometers.

White-light emission (WLE) from a single molecule is a highly desirable alternative to a complex mixture of complementary colour emitters, which suffers from poor stability and reproducibility for potential use in organic electronic devices and lighting applications. We report single-molecule WLE both in solution and thin films by judiciously controlled π-electron delocalisation between the triarylamine subchromophoric units. Triphenylamine (TPA) forms the central core, and the phenyl rings are substituted with the electron-deficient acceptor 3-ethylrhodanine (Rh) and electron-rich donors triphenylamine or carbazole. The enforced biphenyl configuration of the TPA core and the other donors renders the π-conjugation across the entire chromophore poor, thus the individual subchromophoric units retain their individual emission characteristics, which cover all three primary colour emissions, that is, red, green and blue (RGB). TPA-Rh units exhibit broad fluorescence in the green-red region originating from the local excited (LE) state and intramolecular charge transfer state (ICT), strongly influenced by the solvent, water, and temperature. Different fluorescence parameters, including spectral maxima, ratiometric changes in ICT emission at the expense of blue emission from terminal donor units, and changes in lifetime, have a linear relationship with temperature between 180-330 K, thus the molecules can function as a multiparameter luminescent molecular thermometer. A temperature coefficient of 0.19 K-1 in ratiometric fluorescence changes along with a spectral shift of 0.3 nm K-1 and their workability over the wide temperature makes these molecules promising materials for potential applications. At lower temperatures, individual subchromophoric properties subside because of the reduced dihedral angle of biphenyl, and fluorescence from the whole molecule becomes dominant.

Fluorescence Lifetime Changes Induced by Laser Irradiation: A Preclinical Study towards the Evaluation of Retinal Metabolic States.

Fluorescence Lifetime (FLT) of intrinsic fluorophores may alter under the change in metabolic state. In this study, the FLT of rabbit retina was investigated in vivo after laser irradiation using fluorescence lifetime imaging ophthalmoscopy (FLIO). The retina of the Chinchilla bastard rabbits was irradiated with a 514 nm diode laser. FLIO, fundus photography, and optical coherence tomography (OCT) were conducted 30 min and 1 to 3 weeks after treatment. After strong coagulation, the FLT at laser spots was significantly elongated immediately after irradiation, conversely shortened after more than a week. Histological examination showed eosinophilic substance and melanin clumping in subretinal space at the coagulation spots older than one week. The FLT was also elongated right around the coagulation spots, which corresponded to the discontinuous ellipsoid zone (EZ) on OCT. This EZ change was recovered after one week, and the FLT became the same level as the surroundings. In addition, there was a region around the laser spot where the FLT was temporarily shorter than the surrounding area. When weak pulse energy was applied to selectively destroy only the RPE, a shortening of the FLT was observed immediately around the laser spot within one week after irradiation. FLIO could serve as a tool to evaluate the structural and metabolic response of the retina to laser treatments.

IMAGING ARTIFACTS IN FLUORESCENCE LIFETIME IMAGING OPHTHALMOSCOPY.

To investigate and quantify the influence of imaging artifacts on retinal fluorescence lifetime (FLIO) values and to provide helpful hints and tricks to avoid imaging artifacts and to improve FLIO image acquisition quality. A systematic analysis of potential parameters influencing FLIO quality and/or fluorescence lifetime values was performed in a prospective systematic experimental imaging study in five eyes of five healthy subjects. For image acquisition, a fluorescence lifetime imaging ophthalmoscope (Heidelberg Engineering) was used. Quantitative analysis of FLIO lifetime changes due to imaging artifacts was performed. Imaging artifacts with significant influence on fluorescence lifetimes included too short image acquisition time, insufficient illumination, ocular surface problems, and image defocus. Prior use of systemic or topical fluorescein makes analysis of retinal fluorescence lifetimes impossible. Awareness of possible sources of imaging artifacts is important for FLIO image acquisition and analysis. Therefore, standardized imaging and analysis procedure in FLIO is crucial for high-quality image acquisition and the possibility for systematic quantitative fluorescence lifetime analysis.

Impact of aircraft lifetime change on lifecycle CO2 emissions and costs in Japan

Airline industry CO2 emissions have increased rapidly; air transportation released approximately 2.8% of global fuel-combustion-based CO2 emissions in 2019. Focusing on Japan, this study explored the introduction of new passenger aircraft as a CO2-reduction policy. To this end, the lifetime distribution function for passenger aircraft was specified. Lifecycle CO2 emissions and the associated costs between 1965 and 2019 were then estimated. The results showed that single-aisle aircraft followed a Rayleigh distribution with a mean of 13.42, while twin-aisle aircraft followed a normal distribution with a mean of 19.82. The reduction potential of lifecycle CO2 emissions is 28.2 Mt. over 55 years by extending the lifetime +11 years of single-aisle aircraft and shortening the lifetime −8 years of twin-aisle aircraft. If the average fuel intensity of aircraft inflow improves steadily, the shortened lifetime and introduction of more fuel-efficient aircraft contribute to a decrease in lifecycle CO2 emissions. However, the cost associated with the lifecycle CO2 emission reductions is USD 94.0 billion, and airlines need to pay USD 3.4 thousand to reduce CO2 emissions by one unit. In sum, the introduction of new aircraft was shown to be cost-ineffective as a CO2-reduction policy, and airlines need to switch to less costly alternatives.

Molecular conformation dependence of phosphorescence lifetime in organic aggregates

Organic bulk crystal with room-temperature phosphorescence (RTP) is normally fabricated into nanoparticles (NPs) for biological applications, accompanying with inevitable change in RTP lifetime and molecular conformation. By using molecular dynamics and quantum chemistry methods, the difluoroboron β-diketonate (BF2bdk) compound (Br-NpCzBF2) was explored to uncover the molecular conformation-dependent RTP from crystal to NPs. We proposed that from crystal to amorphous aggregates, the distorted BF2bdk group caused by the weakened intermolecular B–F⋯H–C hydrogen bonds convert the T1 from hybridized local and charge transfer to locally excited states. Such change strengthens the vibronic coupling effect on the CC stretching vibration, and enormously accelerates the nonradiative decay rate of T1→S0 by 1–2 orders of magnitude. Consequently, the RTP lifetime is shortened from 566 μs in crystal to about 10 μs in amorphous aggregates, which is consistent with the experiments. This work provides new insight into the RTP mechanism and opens a novel design avenue for designing organic RTP materials in biological fields.

An underestimated negative cloud feedback from cloud lifetime changes

As the atmosphere warms, part of the cloud population shifts from ice and mixed-phase (‘cold’) to liquid (‘warm’) clouds. Because warm clouds are more reflective and longer-lived, this phase change reduces the solar flux absorbed by the Earth and constitutes a negative radiative feedback. This cooling feedback is weaker in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) than in the fifth phase (CMIP5), contributing to greater greenhouse warming. Although this change is often attributed to improvements in the simulated cloud phase, another model bias persists: warm clouds precipitate too readily, potentially leading to underestimated negative lifetime feedbacks. In this study we modified a climate model to better simulate warm-rain probability and found that it exhibits a cloud lifetime feedback nearly three times larger than the default model. This suggests that model errors in cloud-precipitation processes may bias cloud feedbacks by as much as the CMIP5-to-CMIP6 climate sensitivity difference. Reliable climate model projections therefore require improved cloud process realism guided by process-oriented observations and observational constraints. CMIP6 models simulate higher and more accurate cloud liquid water fraction relative to CMIP5, but both ensembles overestimate warm cloud precipitation. Correcting these warm cloud processes in a model exposes compensating biases large enough to offset CMIP5–CMIP6 climate sensitivity differences.

Abstract P-10: Solvatochromic Fluorescent Dyes Tested for Spectroscopic Measurements of Protein Conformational Dynamics

Background: Recoverin is a 23 kDa protein, belonging to the superfamily of EF-hand Ca2+-binding proteins. One of the functions of recoverin is to regulate the activity of the rhodopsin kinase GRK1, which regulates the activity of rhodopsin. In dim ambient light, the level of calcium in the rod cells of the retina is high, so recoverin binds to and inhibits rhodopsin kinase, leaving rhodopsin very sensitive to photons to enable the eye to detect visual signals even under low-light conditions. Many biophysical methods have previously been used to study the conformational dynamics of recoverin, including NMR, SPR and fluorescence spectroscopy. Here we describe fluorescent solvatochromic dyes suitable for spectroscopic observation of conformational changes in recoverin. Methods: We tested four fluorescent dyes, which were covalently attached to Cys39 of recoverin via the thiol-maleimide interaction. Results: Two out of four labeled recoverin samples showed EGTA-induced changes in the fluorescence lifetime and excitation and emission spectra. Conclusion: Our experiments show solvatochromic fluorescent dyes that can be successfully used for spectroscopic observation of conformational dynamics in proteins.

Abstract P-17: Photophysical Properties of Freely Diffusing and Immobilized Fluorescent Conjugate Based on Calcium-Binding Protein Recoverin and Alexa647 Dye

Background: Recoverin is a calcium sensor membrane-associated protein that inhibits rhodopsin kinase thereby participating in the regulation of visual transduction. Here we examined calcium-induced conformational changes in recoverin conjugated with fluorescent dye Alexa647. Methods: Photophysical properties of immobilized and freely diffusing recoverin were investigated using fluorescence lifetime imaging microscopy and fluorescence emission spectroscopy. In solution, the formation and dissociation of the Ca2+-recoverin complex manifested as changes in Alexa647 spectra and the lifetime. In contrast, immobilization of recoverin on the microscopy glass via biotin–NeutrAvidin–biotinylated polyethylene glycol (PEG) tether inhibited changes in fluorescent signal. That can be provided by PEG as it prevented the calcium-induced changes in spectrum and lifetime of recoverin-bound Alexa647 in solution. The use of another immobilization facilitator, bovine serum albumin (BSA), did not affect calcium-induced changes in fluorescence of the conjugate in solution but produced the matrix, which was ineffective in recoverin immobilization. Results: Microscale thermophoresis demonstrated that biotinylated recoverin interacted with NeutrAvidin in solution indicating that immobilization affinity depended mainly on the geometry of the glass coating surface. Conclusion: Our results highlight the challenge of specific protein immobilization that does not affect protein functionality. By the example of recoverin, we showed that the employment of two common immobilization facilitators, PEG and BSA, yielded surfaces with different space geometry, which differently affect NeutrAvidin-based immobilization affinity as well as Ca2+-dependent conformational changes of the biotinylated protein.

Extracellular pH affects the fluorescence lifetimes of metabolic co-factors.

.Significance: Autofluorescence measurements of the metabolic cofactors NADH and flavin adenine dinucleotide (FAD) provide a label-free method to quantify cellular metabolism. However, the effect of extracellular pH on flavin lifetimes is currently unknown.Aim: To quantify the relationship between extracellular pH and the fluorescence lifetimes of FAD, flavin mononucleotide (FMN), and reduced nicotinamide adenine dinucleotide (phosphate) [NAD(P)H].Approach: Human breast cancer (BT474) and HeLa cells were placed in pH-adjusted media. Images of an intracellular pH indicator or endogenous fluorescence were acquired using two-photon fluorescence lifetime imaging. Fluorescence lifetimes of FAD and FMN in solutions were quantified over the same pH range.Results: The relationship between intracellular and extracellular pH was linear in both cell lines. Between extracellular pH 4 to 9, FAD mean lifetimes increased with increasing pH. NAD(P)H mean lifetimes decreased with increasing pH between extracellular pH 5 to 9. The relationship between NAD(P)H lifetime and extracellular pH differed between the two cell lines. Fluorescence lifetimes of FAD, FAD-cholesterol oxidase, and FMN solutions decreased, showed no trend, and showed no trend, respectively, with increasing pH.Conclusions: Changes in endogenous fluorescence lifetimes with extracellular pH are mostly due to indirect changes within the cell rather than direct pH quenching of the endogenous molecules.

Highly selective fluorometric detection of para-nitrophenol from its isomers by nitrogen-doped graphene quantum dots

Nitrogen-doped graphene quantum dots (N-GQDs) with blue fluorescence and excellent water-solubility and an average diameter of approximately 21 nm have been prepared via hydrothermal treatment of ammonium fluoroborate and trisodium citrate, with the average size in diameter about 21 nm. It was found that para-nitrophenol (4-NP) could dramatically quench the fluorescence of N-GQDs via static quenching because the good linearity of the Stern-Volmer equation (kq ≫ 2.0 × 1010L/(mol·s)) and the change in lifetime before and after the addition of 4-NP, which are different from that of its isomers and other analogs or metal ions. A fast and direct fluorimetric method with N-GQDs probe has thereby been developed for detecting 4-NP at concentrations from 0 to 20 μM, with a limit of detection of 0.29 μM. Furthermore, this proposed fluorimetric method was successfully applied to analyze 4-NP in real water samples, showing the feasible detection of trace 4-NP in complicated environmental water samples. The developed N-GQDs-based fluorimetric method is expected to be applied to the highly selective determination of 4-NP from its isomers, other analogs and general metal ions.

Fluorescence lifetime imaging microscopy and time-resolved anisotropy of nanomaterial-induced changes to red blood cell membranes

With the use of engineered nano-materials (ENM) becoming more prevalent, it is essential to determine potential human health impacts. Specifically, the effects on biological lipid membranes will be important for determining molecular events that may contribute to both toxicity and suitable biomedical applications. To better understand the mechanisms of ENM-induced hemolysis and membrane permeability, fluorescence lifetime imaging microscopy (FLIM) was performed on human red blood cells (RBC) exposed to titanium dioxide ENM, zinc oxide ENM, or micron-sized crystalline silica. In the FLIM images, changes in the intensity-weighted fluorescence lifetime of the lipophilic fluorescence probe Di-4-ANEPPDHQ were used to identify localized changes to membrane. Time-resolved fluorescence anisotropy and FLIM of RBC treated with methyl-ß-cyclodextrin was performed to aid in interpreting how changes to membrane order influence changes in the fluorescence lifetime of the probe. Treatment of RBC with methyl-ß-cyclodextrin caused an increase in the wobble-in-a-cone angle and shorter fluorescence lifetimes of di-4-ANEPPDHQ. Treatment of RBC with titanium dioxide caused a significant increase in fluorescence lifetime compared to non-treated samples, indicating increased membrane order. Crystalline silica also increased the fluorescence lifetime compared to control levels. In contrast, zinc oxide decreased the fluorescence lifetime, representing decreased membrane order. However, treatment with soluble zinc sulfate resulted in no significant change in fluorescence lifetime, indicating that the decrease in order of the RBC membranes caused by zinc oxide ENM was not due to zinc ions formed during potential dissolution of the nanoparticles. These results give insight into mechanisms for how these three materials might disrupt RBC membranes and membranes of other cells. The results also provide evidence for a direct correlation between the size, interaction-available surface area of the nano-material and cell membrane disruption.

11‐2: Technology Developments in High‐Resolution FMM‐free OLED and BEOL IGZO TFTs for Power‐Efficient Microdisplays

Resolution, power efficiency, and brightness are crucial features in microdisplays for upcoming VR and AR applications. This presentation shows our work towards a high‐resolution direct RGB microdisplay. An IGZO TFTs with a top gate length of 80 nm is realized with 300mm facilities for high‐resolution backplane developments. For the development of high‐resolution OLED enabled by photolithographic patterning, we investigate an excess driving voltage in photolithographic patterned OLEDs caused by contaminants at the organic semiconductor interface. With necessary mitigation, we reduce the excess driving voltage and observe no significant lifetime change after multiple photolithographic patterning steps.

The Influence of Cataract on Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO).

PurposeTo investigate the influence of lens opacifications on fluorescence lifetime imaging ophthalmoscopy (FLIO).MethodsForty-seven eyes of 45 patients were included. Mean fluorescence lifetimes (Tm) were recorded with a fluorescence lifetime imaging ophthalmoscope in a short spectral channel (SSC) and a long spectral channel (LSC). Retinal and lens autofluorescence lifetimes were measured in subjects before and after cataract surgery. Lens opacification was graded using the Lens Opacities Classification System III (LOCS III) classification.ResultsThe retinal Tm decreased significantly after cataract surgery in both spectral channels (SSC: –53%, P < 0.0001; LSC: –26%, P = 0.0041). The lens Tm differed significantly between the crystalline and the artificial lens in both spectral channels (P < 0.0001). The “nuclear opacity” and “nuclear color” score of the LOCS III classification correlated significantly with the mean Tm difference in both spectral channels (P < 0.0001).ConclusionsLens opacification results in significantly longer retinal Tm. Therefore the lens status has to be considered when performing cross-sectional fluorescence lifetime analysis. Cataract-formation and cataract-surgery needs to be considered when conducting longitudinal studies. Grading of nuclear opacity following the LOCS III classification provides an approximate conversion formula for the mean change of lifetimes, which can be helpful in the interpretation of data in patients with lens opacities.Translational RelevanceFLIO is significantly influenced by lens opacities. Using a lens opacity grading scheme and measuring fluorescence lifetimes before and after cataract surgery, an approximative conversion formula can be calculated, which enables the comparison of lifetimes after cataract surgery or over the course of time.

Biosensing the Presence of Metal Nanoparticles by Spectrally- and Time-Resolved Endogenous Fluorescence in Water Moss Fontinalis antipyretica

Pollution by heavy metals represents a significant environmental burden. We employed confocal microscopy with spectral detection and fluorescence lifetime imaging (FLIM) to evaluate the effect of nanoparticles (NPs) from various metals (Zinc, Nickel, Cobalt, Copper) on endogenous fluorescence of Fontinalis antipyretica moss. Short term (3–5 day) exposure to NPs, designed and fabricated by direct synthesis using femtosecond laser ablation in water, was studied. The green flavonoid and/or lignin endogenous fluorescence peaking between 500 and 560 nm was found to be increased by Zn and significantly reduced by Cu. The overall red chlorophyll fluorescence intensity with a maximum of 680 nm remained largely unchanged after exposure to Ni and Zn, but was decreased in the presence of Co and completely abolished by Cu. All NPs but Zn induced changes in the fluorescence lifetimes, demonstrating increased sensitivity of this parameter to environmental pollution. Gathered data indicate fast responsiveness of the endogenous fluorescence in the Fontinalis antipyretica moss to the presence of heavy metals that can thus potentially serve as a biosensing tool for monitoring environmental pollution in the moss natural environment.

Self-Induced Dark States in Two-Dimensional Excitons

We have obtained an ultralong lifetime exciton emission in InAs/GaAs single quantum dots (QDs) when the QD films are transferred onto the Si substrate covered by Ag nanoparticles. It is found that when the separation distance from the QD layer (also the wetting layer) to the Ag nanoparticles is around 19 nm, the QD emission lifetime changes from approximately 1 to 2000 ns. A classical dipole oscillator model is used to quantitatively calculate the spontaneous radiation decay rate of the excitons in the wetting layer (WL), and the simulated calculation result is in good agreement with the experimental one, revealing that the long lifetime exciton emission is due to the existence of the dark state in the WL. The self-induced dark state stems from the destructive interference between the exciton emission field and the induced dipole field of the Ag nanoparticles.

Cost-Effectiveness of Combination Therapy for Patients With Systemic Sclerosis-Related Pulmonary Arterial Hypertension.

BackgroundTo evaluate the cost‐effectiveness of combination pulmonary arterial hypertension specific therapy in systemic sclerosis–related PAH.Methods and ResultsHealth outcomes and costs were captured through data linkage. Health utility was derived from Medical Outcomes Study Short Form‐36 scores. A probabilistic discrete‐time model was developed to simulate lifetime changes in costs and health utility. Mortality was predicted using a Gompertz parametric survival model. For both treatment arms, the simulations were started using the same cohort of 10 000 patients. Probabilistic sensitivity analysis was performed using the Monte Carlo simulation with 1000 sets of sampled parameter values. Of 143 patients with systemic sclerosis–related pulmonary arterial hypertension, 89 were on monotherapy and 54 on combination therapy. Mean simulated costs per patient per year in monotherapy and combination therapy groups were AU$23 411 (US$16 080) and AU$29 129 (US$19 982), respectively. Mean life years and quality‐adjusted life years from pulmonary arterial hypertension diagnosis to death of patients receiving monotherapy were 7.1 and 3.0, respectively, and of those receiving combination therapy were 9.2 and 3.9, respectively. Incremental costs per life year and quality‐adjusted life year gained of combination therapy compared with monotherapy were AU$47 989 (US$32 920) and AU$113 823 (US$78 082), respectively. At a willingness‐to‐pay threshold of AU$102 000 (US$69 972) per life year gained, and of AU$177 222 (US$121 574) per quality‐adjusted life year gained, the probability of combination therapy being cost‐effective was 0.95.ConclusionsThe incremental cost per quality‐adjusted life year gained of combination therapy compared with monotherapy was substantial in the base case analysis. Given the fatal prognosis of systemic sclerosis–related pulmonary arterial hypertension and the incremental cost per life year of AU$47 989 (US$32 920), combination therapy could be considered cost‐effective in systemic sclerosis–related pulmonary arterial hypertension.

Enhanced detection of oral dysplasia by structured illumination fluorescence lifetime imaging microscopy

We demonstrate that structured illumination microscopy has the potential to enhance fluorescence lifetime imaging microscopy (FLIM) as an early detection method for oral squamous cell carcinoma. FLIM can be used to monitor or detect changes in the fluorescence lifetime of metabolic cofactors (e.g. NADH and FAD) associated with the onset of carcinogenesis. However, out of focus fluorescence often interferes with this lifetime measurement. Structured illumination fluorescence lifetime imaging (SI-FLIM) addresses this by providing depth-resolved lifetime measurements, and applied to oral mucosa, can localize the collected signal to the epithelium. In this study, the hamster model of oral carcinogenesis was used to evaluate SI-FLIM in premalignant and malignant oral mucosa. Cheek pouches were imaged in vivo and correlated to histopathological diagnoses. The potential of NADH fluorescence signal and lifetime, as measured by widefield FLIM and SI-FLIM, to differentiate dysplasia (pre-malignancy) from normal tissue was evaluated. ROC analysis was carried out with the task of discriminating between normal tissue and mild dysplasia, when changes in fluorescence characteristics are localized to the epithelium only. The results demonstrate that SI-FLIM (AUC = 0.83) is a significantly better (p-value = 0.031) marker for mild dysplasia when compared to widefield FLIM (AUC = 0.63).

Change in the Positron Annihilation Lifetime of Vacancy Clusters Containing Hydrogen Atoms in Electron-Irradiated F82H

The change in the positron annihilation lifetime (PAL) of vacancy clusters before and after electrolysis hydrogen charging was determined using PAL measurements in electron-irradiated F82H. The experimental change indicated 8 hydrogen atoms were trapped in vacancy clusters; whereas the theoretical calculation resulted in approximately 14 atoms. As the samples were left at room temperature for 5 min until the start of the PAL measurements, the de-trapping effect of hydrogen atoms was also considered; approximately 13 hydrogen atoms were captured at each vacancy cluster. The PAL decreased after annealing at 148 K, which could not be explained theoretically. Therefore, further experiments and discussions are needed to obtain a precise change in the PAL of vacancy clusters containing hydrogen atoms in F82H.

Gradual Degradation of InGaAs LEDs: Impact on Non-Radiative Lifetime and Extraction of Defect Characteristics.

We present a detailed analysis of the gradual degradation mechanisms of InGaAs Light-Emitting Diodes (LEDs) tuned for optical emission in the 1.45–1.65 μm range. Specifically, we propose a simple and effective methodology for estimating the relative changes in non-radiative lifetime, and a procedure for extracting the properties of defects responsible for Shockley-Read-Hall recombination. By means of a series of accelerated aging experiments, during which we evaluated the variations of the optical and electrical characteristics of three different families of LEDs, we were able to identify the root causes of device degradation. Specifically, the experimental results show that, both for longer stress time at moderate currents or for short-term stress under high injection levels, all the devices are affected: (i) by a partial recovery of the optical emission at the nominal bias current; and (ii) by a decrease in the emission in low-bias regime. This second process was deeply investigated, and was found to be related to the decrease in the non-radiative Shockley-Read-Hall (SRH) lifetime due to the generation/propagation of defects within the active region of the LEDs. Devices tuned for longer-wavelength emission exhibited a second degradation process, which was found to modify the carrier injection dynamics and further speed-up optical degradation in the low bias regime. These processes were ascribed to the effects of a second non-radiative recombination center, whose formation within the active region of the device was induced by the aging procedure. Through mathematical analysis of the degradation data, we could quantify the percentage variation in SRH lifetime, and identify the activation energy of the related defects.