Variation Of Lifetime Research Articles

Carrier Dynamics Mechanisms in Bi‐Based Photocatalytic Materials

Bi‐based nanomaterials have unique physicochemical and structural properties, allowing them to respond to visible light effectively. The Bi‐based semiconductors can be used for degradation of pollutants, reduction of CO2, nitrogen fixation, and decomposition of water, having the strong potential to address environmental pollution and energy shortages. However, the large‐scale application is still limited by the separation and transfer of electron–hole pairs. Herein this review article, carrier dynamics are studied from three perspectives, including structural modulation, atomic conformational reorganization, and surface modification. The relevant mechanisms of different strategies are mainly highlighted, the variations of carrier motion or lifetime are explored, and the progress in practical studies is elucidated. The structural modulation strategy is first introduced, including different dimensional structures and heterogeneous junctions. Further, the atomic conformational reorganization strategy is presented, including Bi‐rich strategies, doping, and vacancy defects. Additionally, the surface modification strategy is outlined, including facet engineering, loading of semiconductor cocatalysts, precious metals, or single atoms. Finally, these strategies are summarized for regulating carrier dynamics and the outlook with the main research trend, providing more inspiration for designing desirable Bi‐based semiconductors.

Application of small perturbation theory for assessing variations of prompt neutron lifetime in a lead-cooled fast reactor

The paper considers the applicability of small perturbation theory to assessing the variations of the prompt neutron lifetime caused by variations in the isotope composition of a lead-cooled fast reactor. The generalized small perturbation theory formulas have been developed to calculate derivatives of the prompt neutron lifetime regarded as a bilinear neutron flux and neutron worth ratio. A numerical algorithm has been proposed for the step-by-step application of the small perturbation theory formulas to assess the prompt neutron lifetime variations caused by a major perturbation in the reactor isotope composition, e.g. by the complete change of the material used earlier as the neutron reflector. The advantage of the proposed approach has been shown which consists in that it is basically possible to determine the role of different neutron reactions, isotopes and energy groups in and their contributions to the total prompt neutron lifetime variation caused by major changes in the reactor isotope composition.

Observation of ~100% valley-coherent excitons in monolayer MoS2 through giant enhancement of valley coherence time

In monolayer transition metal dichalcogenide semiconductors, valley coherence degrades rapidly due to a combination of fast scattering and inter-valley exchange interaction. This leads to a sub-picosecond valley coherence time, making coherent manipulation of exciton a highly challenging task. Using monolayer MoS2 sandwiched between top and bottom graphene, here we demonstrate fully valley-coherent excitons by observing ~100% degree of linear polarization in steady state photoluminescence. This is achieved in this unique design through a combined effect of (a) suppression in exchange interaction due to enhanced dielectric screening, (b) reduction in exciton lifetime due to a fast inter-layer transfer to graphene, and (c) operating in the motional narrowing regime. We disentangle the role of the key parameters affecting valley coherence by using a combination of calculation (solutions of Bethe-Salpeter and Maialle-Silva-Sham equations) and a careful choice of design of experiments using four different stacks with systematic variation of screening and exciton lifetime. To the best of our knowledge, this is the first report in which the excitons are found to be valley coherent in the entire lifetime in monolayer semiconductors, allowing optical readout of valley coherence possible.

Valuation of used machinery based on the new model of its degradation

We propose a new model of equipment degradation. In it, the machine is subjected to random latent failures, the danger of which depends on the equipment condition and after each failure the intensity of the equipment's benefits decreases by a random amount. Equipment that brings negative benefits is subject to decommissioning. The model parameters are found based on known information about the average value and the coefficient of variation of the equipment lifetime. Market value of equipment is determined by discounting the flow of benefits from its future use. This allows us to find the dependence of the equipment’s market value on the benefits it brings. Assessing the market value of new equipment is usually not difficult, but it is much more difficult to do this for used equipment items. Appraisers are usually unable to estimate the value of the work performed by equipment, and when valuing a used equipment, they have to rely on its age. To do this, the market value of a similar new equipment is usually reduced by a depreciation factor or multiplied by Percent Good Factor (PGF, relative value), depending on the age of equipment being valued. However, equipment of the same age may be in different conditions and, therefore, have a different market value. Therefore, such PGFs, in fact, relate to the average equipment that has survived to the appropriate age. Appraisers determine them by formulas or tables that are usually not supported by proper justifications. The proposed model makes it possible to build the dependence of the average PGF on age and calculate the market value of the work performed by machines, even if such works are not traded on the market. It turns out that it is possible to take into account the influence of the utilization cost of the machine and inflation in the model. The results of experimental calculations performed using the model (with calibration parameters selected appropriately) are in good agreement with the market prices of some types of construction equipment.

Atmospheric methane since the last glacial maximum was driven by wetland sources

Abstract. Atmospheric methane (CH4) has changed considerably in the time between the last glacial maximum (LGM) and the preindustrial (PI) periods. We investigate these changes in transient experiments with an Earth system model capable of simulating the global methane cycle interactively, focusing on the rapid changes during the deglaciation, especially pronounced in the Bølling–Allerød (BA) and Younger Dryas (YD) periods. We consider all relevant natural sources and sinks of methane and examine the drivers of changes in methane emissions as well as in the atmospheric lifetime of methane. We find that the evolution of atmospheric methane is largely driven by emissions from tropical wetlands, while variations in the methane atmospheric lifetime are small but not negligible. Our model reproduces most changes in atmospheric methane very well, with the exception of the mid-Holocene decrease in methane, although the timing of ice-sheet meltwater fluxes needs to be adjusted slightly in order to exactly reproduce the variations in the BA and YD.

Joint Prediction of the State of Charge and the State of Health of Lithium-Ion Batteries Based on the PSO-XGBoost Algorithm

Lithium-ion batteries are widely used in power grids as a common form of energy storage in power stations. The state of charge (SOC) and state of health (SOH) reflect the capacity and lifetime variation in the Li-ion batteries, and they are important state parameters of Li-ion batteries. Therefore, the establishment of accurate SOC and SOH prediction models is an essential prerequisite for the correct assessment of the status of lithium batteries, the improvement of the operational accuracy of energy-storage stations, and the development of maintenance plans for energy-storage stations. This paper first analyzes the correlation between SOC and SOH, and then proposes a joint SOC and SOH prediction model using the particle swarm optimization (PSO) algorithm to optimize the extreme gradient boosting algorithm (XGBoost), which takes into account the dynamic correlation between SOC and SOH dynamics, thus enabling more accurate SOC and SOH prediction. Finally, the prediction model is validated using the Oxford battery aging dataset. The correlation between SOC and SOH is verified by comparing the joint prediction results with the SOC individual prediction results. Then, the prediction results of the PSO-XGBoost model, the traditional XGBoost model, and the long short-term memory neural network are compared to verify the effectiveness and accuracy of the PSO-XGBoost model.

Sub-Picosecond Carrier Dynamics Explored using Automated High-Throughput Studies of Doping Inhomogeneity within a Bayesian Framework.

Bottom-up production of semiconductor nanomaterials is often accompanied by inhomogeneity resulting in a spread in electronic properties which may be influenced by the nanoparticle geometry, crystal quality, stoichiometry, or doping. Using photoluminescence spectroscopy of a population of more than 11 000 individual zinc-doped gallium arsenide nanowires, inhomogeneity is revealed in, and correlation between doping and nanowire diameter by use of a Bayesian statistical approach. Recombination of hot-carriers is shown to be responsible for the photoluminescence lineshape; by exploiting lifetime variation across the population, hot-carrier dynamics is revealed at the sub-picosecond timescale showing interband electronic dynamics. High-throughput spectroscopy together with a Bayesian approach are shown to provide unique insight in an inhomogeneous nanomaterial population, and can reveal electronic dynamics otherwise requiring complex pump-probe experiments in highly non-equilibrium conditions.

Spectral imaging in microscopy aids evaluation of the luminescent probe behaviour of europium complexes

In a series of structurally related cationic Eu(III) triamide complexes, the analysis of variations in emission lifetime and spectral signature as a function of probe environment has elucidated the nature of changes to probe speciation. The cationic complexes exhibit an intrinsic tendency to localise in cellular nucleoli or the lysosomes, providing key information in the design and evaluation of related targeted probes. Each of the three complexes studied possesses a coordinated water molecule in aqueous media, that is absent in organic solvents or is displaced by the addition of protein. The complex observed in cellulo is probably a protein-bound Eu complex.

The monks of San Millán: Investigating the transition between pre-monastic and monastic diet using carbon and nitrogen isotope ratios in incremental dentine

From the early Medieval period, Christian monasteries were wealthy and powerful, and played a central role in both religious and political life. Those who entered the monasteries did so at the age of 7–8 years and were drawn from a wide range of social strata. From that point, they were subject to the dietary rules imposed by the rules of each monastic order. In order to assess the origins and diet of 10 monks who lived in the monastery of San Millán de la Cogolla Yuso (La Rioja, Spain) during the 17th – 18th century, collagen from small sections of human dentine (representing the childhood diet) and from ribs (an average of the last 5–10 years of adult diet) was measured to establish lifetime variations in the isotope ratios of carbon (δ13C) and nitrogen (δ15N). Bulk collagen δ13C (overall mean = -18.2‰ +/-0.4) and δ15N (overall mean = 12.6‰ +/-0.8) values from the ribs suggest 2 adult cohorts: one with a diet based on C3 plants and a high intake of protein from meat or dairy products and some marine resources and a second cohort with some C4 plant consumption alongside meat and dairy. Data from the dentine sections revealed different dietary patterns during the period of tooth formation among the monks, suggesting that 4 of them entered the monastery after consuming lower status diets during childhood.

The perishable products case to achieve sustainable food quality and safety goals implementing on-field sustainable supply chain model

Perishable food supply chain required special attention concerning “timely delivery supervision” that may have quality, safety and environmental effects throughout with transportation duration aspects which leads to create economic differences of product value. Consequently, the development of food quality and safety has achieved significant importance. Therefore, the development of perishable food supply chain transportation network needed to more explored to fill the gap of timely supervision. Respectively, the multi-objective conceptual simulation model is developed to optimize the cost, environmental effect, quality and safety, and the appropriate transportation facility at field level connected with perishable food supply chain transportation system. In this study, perishable food lifetime variations are significantly structured as the Weibull random approach, and product perishability is supposed to be influenced by transport refrigerator application, which is assumed as the decision variable. Apart from, multiple vehicle types and multiple perishable food types are taken. The perishable food supply chain case is examined and, the associations and interrelations of all aspects of sustainability are studied, which is known as the multi-objective model of sustainability. According to the findings, by emphasising the cost factors for highly perishable commodities, the supply chain's environmental impact may increase by 108%, and the social impact may rise by 45% for transportation networks with field refrigeration facilities. Additionally, a 23% increase in economic awareness could increase supply chain structure design sustainability by 137%. Environmental impact and the unpredictability of perishable foods are also seen as important variables that might have a variety of effects on the supply chain's structure and operation. This study contributes the cold supply chain's sustainable development objectives while enhancing the quality and safety of perishable products. The results propose that policy makers can significantly decrease the environmental and social effects of the supply chain even without considerably compromising the cost aspect.

Structure and luminescence of a high-efficient blue-red-emitting Na2BaMg(PO4)2: Eu2+, Mn2+ phosphor for plant growth LEDs

New dual-emitting phosphor Na2BaMg(PO4)2: Eu2+, Mn2+ is prepared via conventional sintering method. The structural and luminescent properties of as-synthesized phosphor were systematically studied by experimental characterization and theoretical calculation. Utilizing the Eu2+→Mn2+ energy transfer, this phosphor exhibits efficient double-band emissions at 415 and 620 nm, which has a good match with the absorption spectra of chlorophyll A/B and phytochrome in plants. The energy transfer mechanism had been investigated through emission intensity and decay lifetime variation using Reisfeld's approximation method. Na2BaMg(PO4)2: Eu2+, Mn2+ shows promising properties like good thermal stability (75% emission intensity maintenance at 200 °C) and high quantum efficiency (QE > 80%). A prototype LED was fabricated using optimized phosphor and NUV chip, which exhibits two distinct emission peaks modulating an optimum action spectrum for plant absorption. All results indicate that Na2BaMg(PO4)2: Eu2+, Mn2+ is of great potential as converted component for plant growth LEDs.

The influence of a trap state on the photoluminescence decay times under single pulse excitation

We numerically calculated the time-resolved photoluminescence spectra using the bimolecular trapping-detrapping model. The variations of carrier lifetimes are investigated by changing the carrier recombination and trapping rate constants, as well as the concentration of available trapping states.

Lattice thermal conductivity of topological insulator Bi2Se3 nanocrystals: comparison from theoretical and experimental.

Lattice thermal conductivity (κL) calculations using the Wiedemann-Franz law involve electrical conductivity, which introduces an error in the actual value of κL. We have adopted a non-contact measurement technique and calculated the κL from the temperature and power-dependent Raman spectra of the Bi2Se3 nanocrystals with truncated hexagon plate morphology stabilized in a hexagonal crystal structure. The hexagon plates of Bi2Se3 are 37 to 55 nm thick with lateral dimensions around 550 nm. These Bi2Se3 nanocrystals show three Raman lines, which agree with the theoretical prediction of A11g, E2g and A21g modes. Although the first-order thermal coefficient (-0.016) of Bi2Se3 nanocrystals is quite low, the room temperature κL ∼1.72 W m-1 K-1 is close to the value obtained from the simulation adopting a three-phonon process. The phonon lifetime of Bi2Se3 nanocrystals observed between ∼0.2 ps and 2 ps confirmed carrier-carrier thermalization with a small contribution from electron-electron and intraband electron-longitudinal-optical-phonon relaxation. The variations of phonon lifetime, Gruneisen parameter and κL of the mode frequencies outline the crucial role of the anharmonicity and acoustic-optical phonon scattering in reducing the κL of Bi2Se3. The non-contact measurements and relevant thermal property parameters open up exciting opportunities to address the anharmonic effects in other thermoelectric materials for obtaining a high figure of merit.

PARALLEL MEASUREMENTS OF PROTEIN AND CELL TURNOVER REVEAL HOW TISSUE CONTEXT AND AGING SHAPE PROTEIN LIFETIMES

Abstract The lifespans of proteins can range from moments to years within mammalian tissues. Protein lifespan is relevant to organismal aging, as long-lived proteins can accrue damage over time. It is unclear how protein lifetime is shaped by tissue context, where both cell division and proteolytic degradation contribute to protein turnover. We have developed turnover and replication analysis by 15N isotope labeling (TRAIL) for parallel quantification of protein and cell lifetimes. We have deployed TRAIL over 32 days in 4 mouse tissues to date to quantify cell proliferation with high precision and no toxicity and determine that protein lifespan varies independently of cell lifespan. Variation in protein lifetime is non-random: multiprotein complexes such as the ribosome have consistent lifetimes across tissues, while mitochondria, peroxisomes, and lipid droplets have variable lifetimes across tissues. To model the effects of aging on tissue homeostasis, we apply TRAIL to a mouse model of Hutchinson-Gilford progeria syndrome and uncover fat-specific alterations in cell lifetime and proteome composition, as well as a broad decrease in protein turnover flux. These data indicate that environmental factors influence protein turnover in vivo and provide a framework to understand proteome aging in tissue context.

Positronium chemistry of a Fe2+/3+ solution under electrochemical control.

The positronium chemistry of a Fe2+/3+ solution is studied under full electrochemical control. For this novel approach to positronium electrochemistry, a suitable cell setup is used, which allows simultaneously both electrochemical measurements and positron annihilation spectroscopy. For the Fe2+/3+ redox couple, positronium serves as an ideally suited atomic probe owing to the rather different positronium chemistry of Fe2+ (spin conversion) and Fe3+ (total positronium inhibition and oxidation). This enabled the precise in situ monitoring of oxidation and reduction by means of positron lifetime upon slow cycling voltammetry or galvanostatic charging. The variation of the mean positron lifetime with the Fe2+/3+ concentration ratio could be quantitatively described by a reaction rate model for positronium formation and annihilation. An asymmetric behavior of the variation of the mean positron lifetime with applied potential, as compared to the simultaneously recorded symmetric current-potential curve, could be explained by the stronger influence of Fe3+ on the characteristics of positronium formation and annihilation. The highly reversible galvanostatic charging behavior monitored by positron lifetime underlines the attractive application potentials of positronium electrochemistry for in situ studies of iron-based redox-flow battery electrolytes.

Eu3+-doped CdSe nanocrystals with blueshift emission and high quantum yield

In this work, we used an oil phase method to synthesize Eu3+-doped CdSe nanocrystals (NCs), which were characterized extensively with X-ray powder diffraction (XRD), transmission electron microscopy (TEM), UV–visible (UV–vis) absorption and emission. The CdSe:Eu NCs were monodispersed and uniform spherical nanocrystals with a cubic structure resembling CdSe NCs. The particle diameter depended on the content of the Eu3+ dopant and ranged from 5.57to 4.27 nm, respectively. The CdSe:Eu NCs containing 20 mol% Eu3+ (denoted as a-20) has a 31nm blueshift in absorption and a 25 nm blueshift in emission with comparison to the pure CdSe NCs. The efficiency of energy transfer from CdSe to Eu3+ can be calculated from the variation of fluorescence lifetime to be 22%. The quantum yield (QY) of the CdSe:Eu NCs is the highest when the concentration of the Eu3+ dopant is 20 mol%. High reaction temperature and charge compensation can effectively improve the QY of the CdSe:Eu NCs.

Temperature dependence of the fluorescence lifetime and emission cross section of Tm:YLF in the 78–300 K range

We have investigated the spectroscopic properties of Tm:YLF material around 1900 nm in detail to understand its amplification performance at cryogenic temperatures. Fluorescence lifetime and emission cross section (ECS) measurements are performed in the 78–300 K range using crystals with Tm doping levels of 0.5 and 2.5%. The radiative lifetime of the 3F4 level of Tm:YLF is found to be temperature dependent, and has a value of around 18 ms at 78 K, and 15.25 ms at 300 K, respectively. The emission measurements indicate the presence of rather strong and reasonably broadband peaks even at cryogenic temperatures. The 1877 nm emission peak of the E//c configuration has a strength of around 2.4 × 10−20 cm2 and a full-width half maximum (FWHM) of around 4 nm at 100 K. The E//a axis configuration possesses a broader emission around 1908 nm with a FWHM of around 19 nm at 100 K, but with a lower peak ECS value of 0.75 × 10−20 cm2. We have also investigated the temperature variation of fluorescence lifetime for the 3H4 level, and the results showed that the two-for-one cross-relaxation process is also quite effective at cryogenic temperatures. These findings clearly demonstrate that cryogenic Tm:YLF systems have the potential to reach kW level average powers and sub-1-ps pulsewidths.

Analysis and optimisation of periodic inventory models for perishable items with a general lifetime

We considered two periodic review perishable inventory systems. The first system is controlled by a periodic review policy, where orders are triggered at each review period and when the stock is less than . The second one is controlled by a periodic review policy, where orders are triggered only if the stock level is below . For both models, the lifetime of each product was assumed to follow a general distribution, whereas the lead time was constant. The demands followed a Poisson process, and all unsatisfied demand was lost. Using an approximate solution of the steady-state probabilities of the inventory level, we obtained a closed form of cost expression. Next, we conducted a simulation study to identify our solution accuracy. Finally, we performed a sensitivity analysis to evaluate the effect of the lifetime variation and cost parameters on the best policy and its cost. The obtained results were close to those of the optimal policy with an average accuracy of 3.7% for the periodic review policy and 3.8% for the periodic review policy. For the worst cases, where the accuracy is higher than 7%, we provided an analytical approach to improve the system accuracy.

Developing and adult reef fish show rapid light-induced plasticity in their visual system.

The visual capabilities of fish are optimized for their ecology and light environment over evolutionary time. Similarly, fish vision can adapt to regular changes in light conditions within their lifetime, e.g., ontogenetic or seasonal variation. However, we do not fully understand how vision responds to irregular short-term changes in the light environment, e.g., algal blooms and light pollution. In this study, we investigated the effect of short-term exposure to unnatural light conditions on opsin gene expression and retinal cell densities in juvenile and adult diurnal reef fish (convict surgeonfish; Acanthurus triostegus). Results revealed phenotypic plasticity in the retina across ontogeny, particularly during development. The most substantial differences at both molecular and cellular levels were found under constant dim light, while constant bright light and simulated artificial light at night had a lesser effect. Under dim light, juveniles and adults increased absolute expression of the cone opsin genes, sws2a, rh2c and lws, within a few days and juveniles also decreased densities of cones, inner nuclear layer cells and ganglion cells. These changes potentially enhanced vision under the altered light conditions. Thus, our study suggests that plasticity mainly comes into play when conditions are extremely different to the species' natural light environment, i.e., a diurnal fish in "constant night". Finally, in a rescue experiment on adults, shifts in opsin expression were reverted within 24 h. Overall, our study showed rapid, reversible light-induced changes in the retina of A. triostegus, demonstrating phenotypic plasticity in the visual system of a reef fish throughout life.

Failure by slow crack growth of SiC fibers: Comparing the lifetime scatter for single filaments and multifilament tows

AbstractSiC‐based fibers are subjected to slow crack growth, a crack growth mechanism activated by stresses and the chemical environment, as identified by static fatigue testing. Such tests can be performed on filaments or bundles. Although both types of specimens show a similar lifetime variation, testing of bundles is often preferred. This work compares the scatter of lifetimes predicted for filaments and for tows using a dedicated Monte Carlo simulation tool relying on the following hypotheses: The stress applied to a single filament can be defined, whereas the size of its most critical flaw cannot; on a bundle, neither the applied stress nor the strength of the critical filament (which triggers the cascade failure and the tow failure) can be defined. Depending on the parallelism of fibers inside the bundle and their strength dispersion, the lifetime scatter can be narrower for filaments compared to tows or vice versa.