Influence of optical heterogeneities on reconstruction of spatial phosphorescence lifetime distributions

AbstractWe study a selective sampling scheme in which survival data are observed during a data collection period if and only if a specific failure event is experienced. Individual units belong to one of a finite number of subpopulations, which may exhibit different survival behaviour, and thus cause heterogeneity. Based on a Poisson process model for individual emergence of population units, we derive a semiparametric likelihood model, in which the birth distribution is modeled nonparametrically and the lifetime distributions parametrically, and define maximum likelihood estimators. We propose a Newton–Raphson-type optimization method to address numerical challenges caused by the high-dimensional parameter space. The finite-sample properties and computational performance of the proposed algorithms are assessed in a simulation study. Personal insolvencies are studied as a special case of double truncation and we fit the semiparametric model to a medium-sized dataset to estimate the mean age at insolvency and the birth distribution of the underlying population.

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Biocompatible Ir(III) Complexes as Oxygen Sensors for Phosphorescence Lifetime Imaging

Molecules ◽

10.3390/molecules26102898 ◽

2021 ◽

Vol 26 (10) ◽

pp. 2898

Author(s):

Ilya S. Kritchenkov ◽

Anastasia I. Solomatina ◽

Daria O. Kozina ◽

Vitaly V. Porsev ◽

Victor V. Sokolov ◽

...

Keyword(s):

Near Infrared ◽

Biological Systems ◽

Aqueous Media ◽

Oxygen Sensors ◽

Quantum Yields ◽

Complete Agreement ◽

Phosphorescence Lifetime ◽

Lifetime Imaging ◽

Nir Emission ◽

Phosphorescence Lifetime Imaging

Synthesis of biocompatible near infrared phosphorescent complexes and their application in bioimaging as triplet oxygen sensors in live systems are still challenging areas of organometallic chemistry. We have designed and synthetized four novel iridium [Ir(N^C)2(N^N)]+ complexes (N^C–benzothienyl-phenanthridine based cyclometalated ligand; N^N–pyridin-phenanthroimidazol diimine chelate), decorated with oligo(ethylene glycol) groups to impart these emitters’ solubility in aqueous media, biocompatibility, and to shield them from interaction with bio-environment. These substances were fully characterized using NMR spectroscopy and ESI mass-spectrometry. The complexes exhibited excitation close to the biological “window of transparency”, NIR emission at 730 nm, and quantum yields up to 12% in water. The compounds with higher degree of the chromophore shielding possess low toxicity, bleaching stability, absence of sensitivity to variations of pH, serum, and complex concentrations. The properties of these probes as oxygen sensors for biological systems have been studied by using phosphorescence lifetime imaging experiments in different cell cultures. The results showed essential lifetime response onto variations in oxygen concentration (2.0–2.3 μs under normoxia and 2.8–3.0 μs under hypoxia conditions) in complete agreement with the calibration curves obtained “in cuvette”. The data obtained indicate that these emitters can be used as semi-quantitative oxygen sensors in biological systems.

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Insensitivity of steady-state distributions of generalized semi-Markov processes by speeds

Advances in Applied Probability ◽

10.1017/s0001867800031402 ◽

1978 ◽

Vol 10 (04) ◽

pp. 836-851 ◽

Cited By ~ 2

Author(s):

R. Schassberger

Keyword(s):

Steady State ◽

General System ◽

State Distribution ◽

Lifetime Distributions ◽

State Dependent ◽

Semi Markov Process ◽

Semi Markov Processes ◽

Infinite State ◽

State Case ◽

Residual Lifetimes

A generalized semi-Markov process with speeds describes the fluctuation, in time, of the state of a certain general system involving, at any given time, one or more living components, whose residual lifetimes are being reduced at state-dependent speeds. Conditions are given for the stationary state distribution, when it exists, to depend only on the means of some of the lifetime distributions, not their exact shapes. This generalizes results of König and Jansen, particularly to the infinite-state case.

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