Apparent Lifetime Research Articles

Triplet Excited State Mechanistic Study of meso‐Substituted Methylthio Bodipy Derivative: Time‐Resolved Optical and Electron Paramagnetic Resonance Spectral Studies

AbstractUnderstanding the intersystem crossing (ISC) mechanism of organic compounds is essential for designing new triplet photosensitizers. Herein, we investigated the ISC mechanism of a heavy atom‐free Bodipy derivative with thiomethyl substitution (S−BDP). A long‐lived triplet state was observed with nanosecond transient absorption spectroscopy with lifetime of 7.5 ms in a polymer film and 178 μs intrinsic lifetime in fluid solution, much longer as compared with what was previously reported (apparent triplet lifetime=15.5 μs). Femtosecond transient absorption studies retrieved an ISC time constant of ∼3 ns. Time‐resolved electron paramagnetic resonance (TREPR) indicated a special triplet electron spin polarization phase (ESP) pattern (a, e, a, e, a, e) for S−BDP, different from the ESP (e, e, e, a, a, a) typical for the spin‐orbital coupling (SOC) mechanism. This indicates that the electron spin selectivity of the ISC of S−BDP is different from that of the normal SOC effect in iodo‐Bodipy. Simulations of the TREPR spectra give a zero‐field‐splitting D parameter of −2257 MHz, much smaller as compared to the reference 2,6‐diiodo‐Bodipy (D=−4380 MHz). The computed SOC matrix elements (0.28–1.59 cm−1) and energy gaps for the S1/Tn states suggest that the energy matching between the S1 and T2/T3 states (supported by the largest kISC ∼109 s−1) enhances the ISC for this compound.

Chemical characterization of road dust during diwali festival in Guwahati city of Assam, Northeast India.

The present study focuses on the elemental analysis of road dust in Guwahati, the largest city of Assam and the largest metropolis of Northeast India during the Diwali festival. Road dust samples were collected on pre-Diwali (PD), the Day after Diwali (DaD), and one week after Diwali (WaD) from two sites (Lankeshwar; LKW and Patharquarry; PTQ). Three composite samples were collected from 3 points at each site. The elemental concentration was analyzed using inductively coupled plasma mass spectrometry (ICP-MS). The concentrations of Ba and Sr increased by 1.6 and 1.7 times, respectively, after Diwali. Among other firework-related elements (FREs), Mg, Al, K, and Cu increased at LKW following Diwali (both DaD and WaD), whereas Mg, Al, and K increased in DaD dust at PTQ. The average concentration of Traffic Related Elements (TREs) at PTQ was significantly higher than at LKW (p < 0.05; 75.40mg/kg vs 63.96mg/kg). Cd had the highest enrichment (EF), followed by Ni and Zn. EF for Cd, Ni, and Zn ranged from high to extremely high enrichment. Ni and Cd exhibited moderate contamination (CF). The ecological risk (ER) values for Cd at LKW and PTQ were 54.32 and 56.71, respectively, indicating a moderate ER. Pearson's correlation was performed to study the relationship between elements, while PCA analysis was used to identify the main sources of these elements. Although the health hazard indices presently do not suggest any immediate danger, hazard quotient (HQ) values for ingestion, inhalation, and dermal exposure were higher for children than adults. In children, the contribution of HQing to HI (total risk) was the highest, accounting for more than 65% of all elements. There is no apparent lifetime cancer risk due to road dust exposure through inhalation.

Lifetime Suicide Attempts in Otherwise Psychiatrically Healthy Individuals

Not all people who die by suicide have a psychiatric diagnosis; yet, little is known about the percentage and demographics of individuals with lifetime suicide attempts who are apparently psychiatrically healthy. If such suicide attempts are common, there are implications for suicide risk screening, research, policy, and nosology. To estimate the percentage of people with lifetime suicide attempts whose first attempt occurred prior to onset of any psychiatric disorder. This cross-sectional study used data from the US National Epidemiologic Study of Addictions and Related Conditions III (NESARC-III), a cross-sectional face-to-face survey conducted with a nationally representative sample of the US civilian noninstitutionalized population, and included persons with lifetime suicide attempts who were aged 20 to 65 years at survey administration (April 2012 to June 2013). Data from the NESARC, Wave 2 survey from August 2004 to September 2005 were used for replication. Analyses were performed from April to August 2023. Lifetime suicide attempts. The main outcome was presence or absence of a psychiatric disorder before the first lifetime suicide attempt. Among persons with lifetime suicide attempts, the percentage and 95% CI of those whose first suicide attempt occurred before the onset of any apparent psychiatric disorders was calculated, weighted by NESARC sampling and nonresponse weights. Separate analyses were performed for males, females, and 3 age groups (20 to <35, 35-50, and >50 to 65 years). In the total sample of 36 309 respondents, 1948 persons had lifetime suicide attempts; 66.8% (95% CI, 64.1%-69.4%) were female, and 6.2% (95% CI, 4.9%-7.4%) had no apparent lifetime psychiatric diagnoses when surveyed. In addition, 13.4% (95% CI, 11.6%-15.2%) made their first suicide attempt prior to psychiatric disorder onset. Thus, an estimated 19.6% of respondents first attempted suicide without an antecedent psychiatric disorder. No significant age or sex differences were detected in the percentage of those with lifetime suicide attempts absent psychiatric disorders, although females were more likely than males to attempt suicide in the year of psychiatric disorder onset (14.9% [95% CI, 12.5%-17.3%] vs 8.6% [95% CI, 6.0%-11.2%]; P < .001), and attempts were less frequent among those older than 50 to 65 years (3.9% [95% CI, 3.5%-4.4%] vs 6.1% [95% CI, 5.4%-6.8%] for 35-50 years and 6.2% [95% CI, 5.6%-6.9%] for 20 to <35 years; P < .001). In this study, an estimated 19.6% of individuals who attempted suicide did so despite not meeting criteria for an antecedent psychiatric disorder. This finding challenges clinical notions of who is at risk for suicidal behavior and raises questions about the safety of limiting suicide risk screening to psychiatric populations.

When pretty hurts: Beauty premia and penalties in eSports

This paper explores the classic beauty premium paradigm in the eSports Overwatch League. Using two-step probit selection models and unsupervised machine learning algorithms, we find that professional gamers rated as more attractive are more likely to receive a contract in the following year, controlling for productivity and other factors. However, there is no apparent lifetime earnings premium. Regression and cluster analyses reveal that it is not enough to be a good player – the inter-relatedness of productivity, attractiveness, and popularity on social media dictates employability. Looking at the league's wealthiest, most successful, and most appealing teams, we find that attractiveness on its own is a negative predictor of getting hired.

Fatigue degradation of wind turbines considering dynamic wake meandering effects

This paper systematically investigates the effects of six factors, namely wind shear, ambient turbulence, wake meandering, wake-added turbulence, turbulence intensities, and wind speed, on the dynamic responses and fatigue degradation of wind turbines in the wake region. An improved mid-fidelity code, FAST.Farm, is used, which considers wake-added turbulence by adopting an additional wind domain with the Mann model. Different distributions of short-term damage equivalent stresses are found in two selected components, namely figure-8 and elliptical distributions, respectively, for nonturbulent and turbulent inflows at the blade root and a consistent ∞-distribution at the tower section for different inflows. An apparent lifetime reduction is observed at the blade root and tower base after the introduction of ambient turbulence, wake meandering, and wake-added turbulence. This lifetime reduction is more critical at the tower bases of downstream wind turbines, where the fatigue lifetime can be shorter than the designed service lifetime (20 years) owing to the wake effect. Considering a Rayleigh distribution with an average wind speed of 8.5 m/s, the fatigue lifetimes of turbines located 4D and 8D downstream of another turbine are approximately 45.86 % and 13.12 %, respectively, lower than the fatigue lifetime of the upstream turbine, whereas the reductions are 38.80 % and 5.03 %, respectively, for an average wind speed of 10.0 m/s. Given that the wake effect on the fatigue lifetime has already been highlighted in recent design standards, the findings of the present study are expected to provide guidance for fatigue evaluation in practice, which will help improve fatigue estimations, extend turbine lifetimes, and reduce the construction costs.

Observation of Nanoconfinement Effect on the Kinetics of Hydrated Electron in the Nanoscale Water Pools of Water-AOT-Cyclohexane Microemulsions by Picosecond Pulse Radiolysis.

The decay kinetics of the hydrated electron (eaq-) in aerosol OT (AOT)-based ternary microemulsions with pool sizes ranging from 0.34 to 4.85 nm were studied using picosecond pulse radiolysis coupled with transient absorption UV-vis spectroscopy. Electron transfer from oil to water and the subsequent solvation occurred within a time resolution of 7 ps. The decay kinetics of eaq- were accurately modeled using a double-exponential decay model, revealing the occurrence of two types of reactions, i.e., the recombination reaction at the water-oil interface and the radical-radical reactions in the water pools. The apparent lifetimes of both types of decays decreased significantly as the size of water pools decreased, indicating the influence of nanoconfinement effects. Moreover, the importance of the water-oil interface increased with decreasing water content, regardless of the presence or absence of NO3- as an electron scavenger in the water pools. Our findings provide a comprehensive understanding on the kinetics of the radiation reaction in AOT-based microemulsions.

First H- beam extracted from the non-caesiated external RF-coil ion source at ISIS

A high power, high duty-cycle, non-caesiated negative hydrogen ion source is in development at the ISIS pulsed spallation neutron and muon facility. Stable operation of an inductively-coupled plasma pulsing at 50 Hz, 1 ms, 70 kW has been perfected with no apparent lifetime issues. Novel features compared to similar H- sources include a very low power microwave ignition gun, an adjustable permanent magnet filter field and multiple large 3D-printed components. This paper details the initial commissioning efforts required to generate a beam. An H- beam current of 10 mA was extracted on the first try in pure volume-production mode. Parameter sweeps and optimisation to reach the required 35 mA were put on hold to address ancillary equipment problems. Mitigation of RF pickup required major mechanical changes such as additional screening and magnetic shielding. Extraction voltage holding capabilities were investigated to cope with co-extracted electron current loading in excess of 0.7 A. Preliminary studies of the biased plasma electrode current showed that co-extracted electrons could be suppressed by increasing the magnetic filter field and gas flow.

Comment on "Dependence of the Fluorescent Lifetime τ on the Concentration at High Dilution".

A recent Letter in this Journal (Langhals and Schlücker, J. Phys. Chem. Lett. 202213, 7568-7573) reported a dependence of the fluorescence lifetime of a dye on concentration and attributed it to "electromagnetic interactions with distant resonating structures" on a length scale of more than 100 nm. We show that their results can be explained as a straightforward result of absorption and re-emission of the fluorescence ("radiative energy transport"), which lengthens the apparent lifetime at higher concentrations. This effect has been well-documented in the literature many times. We show that simulations of the fluorescence decays accounting for radiative transport can reproduce the authors' results without postulating any new electromagnetic mechanism.

Exciton-exciton annihilation in thin indium selenide layers.

The photocarrier recombination in van der Waals layers may determine the device performance based on these materials. Here, we investigated the photocarrier dynamics in a multilayer indium selenide nanofilm using transient absorption spectroscopy. The sub-bandgap transient absorption feature was attributed to the indirect intraband absorption of the photocarriers, which was then exploited as a probe to monitor the photocarrier dynamics. With increasing pump intensities, the photocarrier decay was accelerated because of the rising contribution from a bimolecular recombination channel that was then assigned to exciton-exciton annihilation. The rate constant of the exciton-exciton annihilation was given as (1.8 ± 0.1) × 10-15cm2ps-1 from a global fitting of the photocarrier decay kinetics for different pump intensities. Our finding suggests that, in contrast with their monolayer counterpart, the exciton-exciton annihilation is rather inefficient in multilayers due to their weaker Coulomb interaction. Hence, compared with monolayers, the lifetime of photocarriers in multilayers would not be significantly reduced under high-intensity pump conditions, and the apparent photocarrier lifetime could be further improved just by suppressing the monomolecular recombination channels such as trapping.

Investigation of defect states in light-irradiated single-crystal ZnO by low-temperature positron annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy of single crystalline ZnO during light illumination has been performed in conjunction with electron spin resonance (ESR) to investigate defects related to persistent photoconductivity. The intensity of the ESR signal changes depending on the light wavelengths and the apparent positron lifetime during red-light illumination is approximately 6 ps lower on average than that during blue-light illumination. The results suggest that the excitation of V O during blue-light illumination increases positively ionized V O, while the relaxation of V O during red-light illumination decreases positively ionized V O, leading to a decrease in the apparent positron lifetime.

Experimental Search for Neutron to Mirror Neutron Oscillations as an Explanation of the Neutron Lifetime Anomaly.

An unexplained >4σ discrepancy persists between "beam" and "bottle" measurements of the neutron lifetime. A new model proposed that conversions of neutrons n into mirror neutrons n^{'}, part of a dark mirror sector, can increase the apparent neutron lifetime by 1% via a small mass splitting Δm between n and n^{'} inside the 4.6T magnetic field of the National Institute of Standards and Technology Beam Lifetime experiment. A search for neutron conversions in a 6.6T magnetic field was performed at the Spallation Neutron Source which excludes this explanation for the neutron lifetime discrepancy.

Influence on the Apparent Luminescent Lifetime of Rare-Earth Upconversion Nanoparticles by Quenching the Sensitizer's Excited State for Hypochlorous Acid Detection and Bioimaging.

Lanthanide-ion-doped upconversion materials have been widely used in biological detection, bioimaging, displays, and anticounterfeiting due to their abilities of real-time readings, high spatial resolution, and deep tissue penetration. The typically long fluorescence lifetimes of rare-earth nanoparticles, in the microsecond to millisecond range, make them useful in interference-free lifetime detection imaging. Most detection systems are accompanied by fluorescence resonance energy transfer (FRET), in which the lifetime of the luminescence center can be used as a signal to reveal the degree of FRET. Due to the complex energy level structure and complex energy transfer processes, the apparent lifetimes of upconversion nanoparticles (UCNPs) do not simply equal the decay time of the corresponding energy level, inducing an insignificant lifetime change in the upconversion detection system. In this study, the relationship between the apparent luminescence lifetime of upconversion and the decay rate of each energy level was studied by numerical simulations. It was proved that the apparent lifetime of the emission at 540 nm was mainly affected by the decay rate of Yb3+. We then constructed a nanocomposite with Rh1000 fluorophores loaded onto the surface of UCNPs to quench the sensitizer Yb3+. We found that the lifetime of the emission at 540 nm from Er3+ was affected to a large extent by the number of attached Rh1000 molecules, proving the greater influence on the apparent luminescent lifetime of Er3+ at 540 nm caused by quenching the Yb3+ excited state. The qualitative detection of hypochlorous acid (HClO) in vivo was also achieved using the luminescent lifetime as the signal.

Do deep marine sediments host unusually stable enzymes?

Microbial life persists in marine sediments up to several kilometers below the sediment-water interface. Microbes in this environment live tremendously slowly, with cell carbon turnover times on the order of years to thousands of years. Those rates are approximately six orders of magnitude slower than fast-growing cells in pure culture. These slow-but-nonzero metabolic rates and long apparent cell lifetimes imply that the enzymes produced by subsurface microbes must be comparably long-lived. Here we present enzyme assays performed in sediments up to 78 meters below the seafloor as part of International Ocean Discovery Program Expedition 347.

A Universal Strategy for Tunable Persistent Luminescent Materials via Radiative Energy Transfer.

In this work, a universal strategy for solid, solution, or gel state organic persistent luminescent materials via radiative energy transfer is proposed. The persistent luminescence (τ>0.7 s) could be remotely regulated between different colors by controlling the isomerization of the energy acceptor. The function relies on the simple radiative energy transfer (reabsorption) mechanism, rather than the complicated communication between the excited state of the molecules such as Förster resonance energy transfer or Dexter energy transfer. And the "apparent lifetime" for the energy acceptor is the same as the lifetime of the energy donor, which was different with a traditional radiative energy transfer process. The simple working principle endows this strategy with huge universality, flexibility, and operability. This work offers a simple, feasible, and universal way to construct various persistent luminescent materials in solid, solution, and gel states.

A Universal Strategy for Tunable Persistent Luminescent Materials via Radiative Energy Transfer

AbstractIn this work, a universal strategy for solid, solution, or gel state organic persistent luminescent materials via radiative energy transfer is proposed. The persistent luminescence (τ&gt;0.7 s) could be remotely regulated between different colors by controlling the isomerization of the energy acceptor. The function relies on the simple radiative energy transfer (reabsorption) mechanism, rather than the complicated communication between the excited state of the molecules such as Förster resonance energy transfer or Dexter energy transfer. And the “apparent lifetime” for the energy acceptor is the same as the lifetime of the energy donor, which was different with a traditional radiative energy transfer process. The simple working principle endows this strategy with huge universality, flexibility, and operability. This work offers a simple, feasible, and universal way to construct various persistent luminescent materials in solid, solution, and gel states.

Extraction of PEDOT:PSS/c‐Si Junction Properties by Modeling of Injection‐Dependent Lifetime Measurements Including Depletion Region Modulation

The carrier lifetime of n‐type silicon wafers coated with the conducting polymer PEDOT:PSS as a function of the excess carrier concentration Δp within the wafer is characterized using the quasi‐steady‐state photoconductance (QSSPC) method, and a drastic increase in the measured apparent lifetime τapp with decreasing Δp is observed. The observed increase with the depletion region modulation (DRM) effect is explained, as PEDOT:PSS‐coated p‐type silicon wafers do not show any increase in lifetime toward low injection levels. By modeling the measured τapp(Δp) curves on n‐type silicon including interface recombination as well as the DRM effect, the interface recombination velocity as well as the band bending Ψs within the silicon induced by PEDOT:PSS are able to be extracted. The impact of adding sorbitol to the PEDOT:PSS dispersion on the τapp(Δp) curves is examined, and it is demonstrated that the admixture of sorbitol improves chemical interface passivation but leaves the band bending within the silicon bulk toward the PEDOT:PSS/c‐Si interface unaffected.

Kinetic Monte Carlo Simulation of Perovskite Solar Cells to Probe Film Coverage and Thickness

Perovskite solar cells (PSCs) have received considerable attention in recent years due to their low processing cost and high‐power conversion efficiency. However, the mechanisms of PSCs are not fully understood. A model based on a probabilistic and statistical approach needs to be developed to simulate, optimize, and predict the photovoltaic (PV) performance of PSC. Herein, the 3D model based on the kinetic Monte Carlo (KMC) approach is developed to simulate 3D morphology of perovskite‐based solar cells and predict their PV performances and charge dynamics. The developed 3D model incorporates the temporal and physical behavior of perovskites, such as charge generation, transport, and recombination. The KMC simulation results show that pin holes‐free perovskite films with a homogenous 400 nm thick perovskite capping layer achieve the highest power conversion efficiency of 20.85%. However, the shortest apparent charge transport time (τt) and the longest apparent charge carrier recombination lifetime (τr) are found for the champion device. PV performance from the fabricated device is used to validate this simulation model. This model can provide a significant conceptual advance in identifying bottlenecks and guiding novel device designs to further improve the performance of perovskite PVs.

Variability in gaseous elemental mercury at Villum Research Station, Station Nord, in North Greenland from 1999 to 2017

Abstract. Mercury is ubiquitous in the atmosphere, and atmospheric transport is an important source for this element in the Arctic. Measurements of gaseous elemental mercury (GEM) have been carried out at Villum Research Station (Villum) at Station Nord, situated in northern Greenland. The measurements cover the period 1999–2017, with a gap in the data for the period 2003–2008 (for a total of 11 years). The measurements were compared with model results from the Danish Eulerian Hemispheric Model (DEHM) that describes the contribution from direct anthropogenic transport, marine emissions and general background concentration. The percentage of time spent over different surfaces was calculated by back-trajectory analysis, and the reaction kinetics were determined by a comparison with ozone. The GEM measurements were analysed for trends, both seasonal and annual. The only significant trends found were negative ones for the winter and autumn months. Comparison of the measurements to simulations using the Danish Eulerian Hemispheric Model (DEHM) indicated that direct transport of anthropogenic emissions of mercury accounts for between 14 % and 17 % of the measured mercury. Analysis of the kinetics of the observed atmospheric mercury depletion events (AMDEs) confirms the results of a previous study at Villum of the competing reactions of GEM and ozone with Br, which suggests that the lifetime of GEM is about a month. However, a GEM lifetime of 12 months gave the best agreement between the model and measurements. The chemical lifetime is shorter, and thus, the apparent lifetime appears to be the result of deposition followed by reduction and re-emission; for this reason, the term “relaxation time” is preferred to “lifetime” for GEM. The relaxation time for GEM causes a delay between emission reductions and the effect on actual concentrations. No significant annual trend was found for the measured concentrations of GEM over the measurement period, despite emission reductions. This is interesting, and together with low direct transport of GEM to Villum as found by the DEHM model, it shows that the dynamics of GEM are very complex. Therefore, in the coming years, intensive measurement networks are needed to describe the global distribution of mercury in the environment as the use of models to predict future levels will still be highly uncertain. The situation is increasingly complex due to global changes that most likely will change the transport patterns of mercury, not only in the atmosphere but also between matrixes.

Nanoscale spatial mapping of charge carrier dynamics in perovskite solar cells

Abstract Charge carrier dynamics and behaviors are key parameters and need to be mapped at the nanoscale in order to search for correct materials for high-performance solar cells. Unfortunately, currently, there are no existing tools or capabilities that can simultaneously map charge carrier dynamics at nanometer range in solar cells. Here we use a Transient Photo-response AFM (TP-AFM) to map for the first time apparent carrier recombination lifetime (τr), transport time (τt) and diffusion length (LD) in hybrid perovskites solar cells. These spatially resolved parameters reveal substantial variations at grain boundaries (GBs) of perovskites. Improved τr, τt and LD at GBs broaden the performance of these state-of-the-art mixed cation perovskites. Detail analysis of these parameters allow us to conclude that reduced density of trap states and recombination in mixed cation perovskites at GBs and its surrounding locations (extending to several nanometers into the grain interior) implies less ion migration. This first of its kind experimental realization of nanoscale mapping of charge carrier dynamics in photovoltaic materials can be used for applications in other optoelectronic devices.

FRET efficiency measurement in a molecular tension probe with a low-cost frequency-domain fluorescence lifetime imaging microscope.

.We demonstrate the possibility of measuring FRET efficiency with a low-cost frequency-domain fluorescence lifetime imaging microscope (FD-FLIM). The system utilizes single-frequency-modulated excitation, which enables the use of cost-effective laser sources and electronics, simplification of data acquisition and analysis, and a dual-channel detection capability. Following calibration with coumarin 6, we measured the apparent donor lifetime in mTFP1-mVenus FRET standards expressed in living cells. We evaluated the system’s sensitivity by differentiating the short and long lifetimes of mTFP1 corresponding to the known standards’ high and low FRET efficiency, respectively. Furthermore, we show that the lifetime of the vinculin tension sensor, VinTS, at focal adhesions () is significantly () longer than the lifetime of the unloaded TSMod probe (). The pixel dwell time was for samples expressing the FRET standards, with signal typically an order of magnitude higher than VinTS. The apparent FRET efficiency () of the standards, calculated from the measured apparent lifetime, was linearly related to their known FRET efficiency by a factor of 0.92 to 0.99 (). This relationship serves as a calibration curve to convert apparent FRET to true FRET and circumvent the need to measure multiexponential lifetime decays. This approach yielded a FRET efficiency of 18% to 19.5%, for VinTS, in agreement with published values. Taken together, our results demonstrate a cost-effective, fast, and sensitive FD-FLIM approach with the potential to facilitate applications of FLIM in mechanobiology and FRET-based biosensing.