Decay Dynamics Research Articles

Hot carrier transfer from plasmon decay in Ag20at H-Si(111) surface: Real-time TDDFT simulation in Wannier gauge.

Plasmon decay is believed to play an essential role in inducing hot carrier transfer at the interfaces between plasmonic nanoparticles and semiconductor surfaces. In this work, we employ real-time time- dependent density functional theory (RT-TDDFT) simulation in the Wannier gauge to gain quantum- mechanical insights into the nonlinear dynamics of the plasmon decay in the Ag20 nanoparticle at a semiconductor surface. The first-principles simulations show that the plasmon decay is more than two times faster when the Ag20 nanoparticle is adsorbed on a hydrogen-terminated Si(111) surface, taking place within 100 femtoseconds of the plasmon excitation. Hot carrier transfer across the interface is observed as the plasmon decay takes place, and nearly 30% of holes are generated deep in the valence band of the semiconductor surface. The use of Wannier gauge in RT-TDDFT simulation is particularly convenient for gaining quantum-mechanical insights into non-equilibrium electron dynamics in complex heterogeneous systems.

Decay Dynamics of Hydrophyte and Nutrient Release in a Lake System: Experimental and Predicting Modeling

Decay Dynamics of Hydrophyte and Nutrient Release in a Lake System: Experimental and Predicting Modeling

A novel simulation of space charge decay dynamics after removing the voltage in epoxy resin composites

Abstract Epoxy resin serves as a critical insulating component in ultra-high voltage dry direct current bushings. However, the accumulation of space charges within the epoxy resin, a byproduct of charge mobility, poses a significant risk to the reliability and operational safety of bushings. Conventional space charge attenuation models, especially after voltage removal, have limited use in simulations aimed at understanding this phenomenon. This study introduces an improved model integrating the bipolar charge transport mechanism with space charge decay based on the hopping conduction mechanism and Schottky’s theorem, establishes a theoretical framework for predicting the space charge behavior following voltage removal, and conducts a simulation to investigate the decay process within the internal structure of epoxy resin and measure the residual charges after voltage removal using the pulsed electro-acoustic method. The experimental data validate the accuracy of the proposed model and theoretical assumptions. The findings show that the remaining negative charges after voltage removal are not enhanced by the field enhancement; the anodic positive and cathodic positive charges are distributed in two-segment discontinuous traps, whereas the negative charges are distributed in one-segment traps. The model identifies two distinct trapping sites for anodic and cathodic positive charges, and one trapping site for negative charges. After voltage removal, when the field strength exceeded 40 kV mm−1, positive charges exist near the upper and lower electrodes, and negative charges exist near the center of the specimen. The consistency between the simulated predictions and experimental data proves the effectiveness of the proposed model in accurately simulating the space charge decay in epoxy materials after voltage removal.

Insights into Ultrafast Relaxation Dynamics of Electronically Excited Furfural and 5-Methylfurfural.

The ultrafast relaxation dynamics of furfural and 5-methylfurfural following excitation in the ultraviolet range is investigated using the femtosecond time-resolved photoelectron spectroscopy method. Specifically, the pump wavelength-dependent decay dynamics of electronically excited furfural and 5-methylfurfural is discussed on the basis of a detailed analysis of our measured time-resolved photoelectron spectroscopy spectra. Irradiation at all pump wavelengths prepares both furfural and 5-methylfurfural molecules with different vibrational levels in the first optically bright S2 (1ππ*) state, the lifetime of which is measured to be at least hundreds of femtoseconds. Besides the prominent deactivation channels of ring-opening and ring-puckering pathways for the S2(1ππ*) state, we propose that there is a minor decay channel of internal conversion from the initially prepared S2(1ππ*) state to the S1(1nπ*) state. The wavepacket decays out of the Franck-Condon region on the S2(1ππ*) state potential energy surface and bifurcates into different parts somewhere. A small fraction of the wavepacket funnels down to the S1(1nπ*) state via internal conversion. The subsequently populated S1(1nπ*) state contains large vibrational excess energy and decays over a lifetime of 2.5-2.8 ps. One of the deactivation channels of the S1(1nπ*) state is intersystem crossing to the 3ππ* triplet state. In addition, methyl substitution effects on the excited-state dynamics of furfural are also discussed. This experimental study provides new insights into the excitation energy-dependent decay dynamics of photoexcited furfural and 5-methylfurfural.

Infrared Fingerprint and Unimolecular Decay Dynamics of the Hydroperoxyalkyl Intermediate (•QOOH) in Cyclopentane Oxidation.

A transient carbon-centered hydroperoxyalkyl intermediate (•QOOH) in the oxidation of cyclopentane is identified by IR action spectroscopy with time-resolved unimolecular decay to hydroxyl (OH) radical products that are detected by UV laser-induced fluorescence. Two nearly degenerate •QOOH isomers, β- and γ-QOOH, are generated by H atom abstraction of the cyclopentyl hydroperoxide precursor. Fundamental and first overtone OH stretch transitions and combination bands of •QOOH are observed and compared with anharmonic frequencies computed by second-order vibrational perturbation theory. An OH stretch transition is also observed for a conformer arising from torsion about a low-energy CCOO barrier. Definitive identification of the β-QOOH isomer relies on its significantly lower transition state (TS) barrier to OH products, which results in rapid unimolecular decay and near unity branching to OH products. A benchmarking approach is utilized to compute high-accuracy stationary point energies, most importantly TS barriers, for cyclopentane oxidation (C5H9O2), building on higher level reference calculations for ethane oxidation (C2H5O2). The experimental OH product appearance rates are compared with computed statistical microcanonical rates using RRKM theory, including heavy-atom tunneling, thereby validating the computed TS barrier. The results are extended to thermal unimolecular decay rate constants at temperatures and pressures relevant to cyclopentane combustion via master-equation modeling. The various torsional and ring puckering states of the wells and transition states are explicitly considered in these calculations.

Differences in HIV-1 reservoir size, landscape characteristics and decay dynamics in acute and chronic treated HIV-1 Clade C infection.

Background Persisting HIV reservoir viruses in resting CD4 T cells and other cellular subsets are the main barrier to cure efforts. Antiretroviral therapy (ART) intensification by early initiation has been shown to enable post-treatment viral control in some cases but the underlying mechanisms are not fully understood. We hypothesized that ART initiated during the hyperacute phase of infection before peak will affect the size, decay dynamics and landscape characteristics of HIV-1 subtype C viral reservoirs. Methods We studied 35 women at high risk of infection from Durban, South Africa identified with hyperacute HIV infection by twice weekly testing for plasma HIV-1 RNA. Study participants included 11 who started ART at a median of 456 (297-1203) days post onset of viremia (DPOV), and 24 who started ART at a median of 1 (1-3) DPOV. We used peripheral blood mononuclear cells (PBMC) to measure total HIV-1 DNA by ddPCR and to sequence reservoir viral genomes by full length individual proviral sequencing (FLIP-seq) from onset of detection of HIV up to 1 year post treatment initiation. Results Whereas ART in hyperacute infection blunted peak viremia compared to untreated individuals (p<0.0001), there was no difference in total HIV-1 DNA measured contemporaneously (p=0.104). There was a steady decline of total HIV DNA in early treated persons over 1 year of ART (p=0.0004), with no significant change observed in the late treated group. Total HIV-1 DNA after one year of treatment was lower in the early treated compared to the late treated group (p=0.02). Generation of 697 single viral genome sequences revealed a difference in the longitudinal proviral genetic landscape over one year between untreated, late treated, and early treated infection: the relative contribution of intact genomes to the total pool of HIV-1 DNA after 1 year was higher in untreated infection (31%) compared to late treated (14%) and early treated infection (0%). Treatment initiated in both late and early infection resulted in a more rapid decay of intact (13% and 51% per month) versus defective (2% and 35% per month) viral genomes. However, intact genomes were still observed one year post chronic treatment initiation in contrast to early treatment where intact genomes were no longer detectable. Moreover, early ART reduced phylogenetic diversity of intact genomes and limited the seeding and persistence of cytotoxic T lymphocyte immune escape variants in the reservoir. Conclusions Overall, our results show that whereas ART initiated in hyperacute HIV-1 subtype C infection did not impact reservoir seeding, it was nevertheless associated with more rapid decay of intact viral genomes, decreased genetic complexity and immune escape in reservoirs, which could accelerate reservoir clearance when combined with other interventional strategies.

Sewer transport conditions and their role in the decay of endogenous SARS-CoV-2 and pepper mild mottle virus from source to collection

This study presents a comprehensive analysis of the decay patterns of endogenous SARS-CoV-2 and Pepper mild mottle virus (PMMoV) within wastewaters spiked with stool from infected patients expressing COVID-19 symptoms, and hence explores the decay of endogenous SARS-CoV-2 and PMMoV targets in wastewaters from source to collection of the sample. Stool samples from infected patients were used as endogenous viral material to more accurately mirror real-world decay processes compared to more traditionally used lab-propagated spike-ins. As such, this study includes data on early decay stages of endogenous viral targets in wastewaters that are typically overlooked when performing decay studies on wastewaters harvested from wastewater treatment plants that contain already-degraded endogenous material. The two distinct sewer transport conditions of dynamic suspended sewer transport and bed and near-bed sewer transport were simulated in this study at temperatures of 4 °C, 12 °C and 20 °C to elucidate decay under these two dominant transport conditions within wastewater infrastructure. The dynamic suspended sewer transport was simulated over 35 h, representing typical flow conditions, whereas bed and near-bed transport extended to 60 days to reflect the prolonged settling of solids in sewer systems during reduced flow periods. In dynamic suspended sewer transport, no decay was observed for SARS-CoV-2, PMMoV, or total RNA over the 35-h period, and temperature ranging from 4 °C to 20 °C had no noticeable effect. Conversely, experiments simulating bed and near-bed transport conditions revealed significant decreases in SARS-CoV-2 and total RNA concentrations by day 2, and PMMoV concentrations by day 3. Only PMMoV exhibited a clear trend of increasing decay constant with higher temperatures, suggesting that while temperature influences decay dynamics, its impact may be less significant than previously assumed, particularly for endogenous RNA that is bound to dissolved organic matter in wastewater. First order decay models were inadequate for accurately fitting decay curves of SARS-CoV-2, PMMoV, and total RNA in bed and near-bed transport conditions. F-tests confirmed the superior fit of the two-phase decay model compared to first order decay models across temperatures of 4 °C–20 °C. Finally, and most importantly, total RNA normalization emerged as an appropriate approach for correcting the time decay of SARS-CoV-2 exposed to bed and near-bed transport conditions. These findings highlight the importance of considering decay from the point of entry in the sewers, sewer transport conditions, and normalization strategies when assessing and modelling the impact of viral decay rates in wastewater systems. This study also emphasizes the need for ongoing research into the diverse and multifaceted factors that influence these decay rates, which is crucial for accurate public health monitoring and response strategies.

Rise and Decay of Photoluminescence in Upconverting Lanthanide-Doped Nanocrystals.

Nanocrystals (NCs) doped with lanthanides are capable of efficient photon upconversion, i.e., absorbing long-wavelength light and emitting shorter-wavelength light. The internal processes that enable upconversion are a complex network of electronic transitions within and energy transfer between dopant centers. In this work, we study the rise and decay dynamics of upconversion emission from β-NaYF4 NCs codoped with Er3+ and Yb3+. The rise dynamics of the red and green upconverted emissions are nonlinear, reflecting the nonlinear nature of upconversion and revealing the mechanisms that populate the emitting states. The excited-state decay dynamics are nonexponential. We unravel the underlying decay pathways using photonic experiments. These reveal the contributions of different upconversion pathways visually, as each pathway exhibits a distinct response to systematic variation of the local density of optical states. Moreover, the effect of the local density of optical states on core-only NCs is qualitatively different from core-shell NCs. This is due to the different balance between feeding and decay of the electronic levels that produce upconverted emission. The understanding of the upconversion dynamics provided here could lead to better imaging and sensing methods relying on upconversion lifetimes or guide the rational optimization of the dopant concentrations for brighter upconversion.

False vacuum decay and nucleation dynamics in neutral atom systems

False vacuum decay and nucleation dynamics in neutral atom systems

Nano‐Size Effects on Decay Dynamics of Photo‐Excited Polarons in CeO2

AbstractThe study of polaron dynamics in complex materials has garnered significant attention owing to its implications for various technological applications, including catalysis, solid‐state devices, and energy storage. This paper investigates the photo‐excited electron and hole polaron dynamics in cerium dioxide (CeO2) using time‐resolved X‐ray absorption spectroscopy, with an emphasis on the nano‐size effect. Additionally, density functional theory and multiplet calculations have been utilized to reveal the photo‐excited polaron dynamics in CeO2 single crystal (SC) and nanocrystal (NC). The electron polaron is observed to decay into a deep trap site with a short duration of ≈5 ps, while electrons in the traps stay for more than 1400 ps. The most significant observation is the behavior of holes in NC, which tends to stay longer (≈150 ps) compared to SC (&lt;10 ps) suggesting hole existence more at the surface than at bulk. The fast dissociation of the electron polarons the prolonged lifetime of the electrons above the Fermi level and the enhanced hole lifetime at the surface are proposed to be among the various factors that influence the high reactivity of CeO2.

Study of angular observables in exclusive semileptonic Bc decays

In this work, we investigate angular observables such as the longitudinal polarization of charged leptons, τ-polarization, and forward-backward asymmetry in semileptonic Bc decays. Additionally, we provide predictions for lepton flavor violating observables, the R ratios in the decay channels Bc→ηc(J/ψ)lνl and Bc→D(D*)lνl across the entire q2 region. Our analysis is conducted within the relativistic independent quark model, focusing on the potential model-dependent aspects of these observables. We compare our model predictions with existing lattice predictions, highlighting the strong applicability of our framework in describing Bc decays. Considering the forthcoming experimental upgrades and the Run 3 data results on Bc meson decays, rapid confirmation of these quantities could indicate significant discoveries of physics beyond the Standard Model. This may open up new avenues for understanding the complex flavor dynamics in heavy meson decays. Published by the American Physical Society 2024

Chemoexcited Formation and Radiationless Decay Dynamics of Firefly Chromophore.

Multistate nonadiabatic dynamics combined with Mixed-Reference Spin-Flip Time-Dependent Density Functional Theory (MRSF-TDDFT) were performed to investigate the chemoexcitation dynamics of firefly dioxetanone (FDO- in S0) to oxyluciferin (OxyLH- in S1) and its subsequent decay dynamics. The formation of oxyluciferin occurs within approximately 100 fs and is primarily controlled by oscillatory CO2 decarboxylation. Unexpected radiationless decay from oxyluciferin was also observed, facilitated by intramolecular rotation. Simulations under three thermal conditions reveal that higher initial thermal energy not only enhances the formation of oxyluciferin but also increases radiationless decay by surpassing barriers to the ground state. Conversely, lower thermal energy conditions reduce oxyluciferin formation but suppress radiationless decay. These findings suggest that optimal conditions for higher chemiluminescence quantum yield involve initial high thermal energy to accelerate CO2 decarboxylation and gradual thermal dissipation to prevent intramolecular rotation of oxyluciferin. This approach could enhance the chemiluminescence quantum yield beyond the current limit of 40%, offering significant potential for applications in biological imaging and analytical chemistry.

Dynamics of wood decay in the cross-section of logs as a result of long-term storage in a landing yard

Dynamics of wood decay in the cross-section of logs as a result of long-term storage in a landing yard

CP violation of baryon decays with N π rescatterings* *Supported in part by the Natural Science Foundation of China (12335003), and the Fundamental Research Funds for the Central Universities (lzujbky-2024-oy02, lzujbky-2023-it12)

There is a long-standing puzzle that the CP violation (CPV) in the baryon systems has never been well established in experiments, while the CPV of mesons have been observed by decades. In this paper, we propose that the CPV of baryon decays can be generated with the rescatterings of a nucleon and a pion into some final states, i.e. or . Benefited by the fruitful data of scatterings, we can model-independently analyse the strong phases of -baryon decays using the partial wave amplitudes of scatterings. Avoiding the most difficult problem of non-perturbative dynamics, it makes a great advantage to predict the CPV of baryon decays with a relatively reliable understanding of the decay dynamics. We study the processes of and with or . It is found that the global CPV of the above processes in the invariant mass regions of scatterings are at the order of several percent. More importantly, the local CPV in some regions of the Dalitz plots can reach the order of 10%, or be even larger. Considering the predicted results and the experimental data samples, we strong suggest to measure the CPV of , which has a large possibility to achieve the first observation of CPV in the baryon system.

Sensing of p-nitrophenol using highly selective and sensitive Boran, Nitrogen doped quantum dots

p-Nitrophenol (PNP) is a nitroaromatic compound that poses a significant threat to human health and the environment due to its carcinogenic, mutagenic, cytotoxic, and embryotoxic properties at low concentrations. Therefore, the selective and sensitive detection of PNP is crucial for both human health and environmental monitoring. Boron (B) and Nitrogen (N) doped quantum dots (B,NQDs) have been found to be effective as blue-green luminescent materials for this purpose. These B,NQDs were synthesized using a one-step hydrothermal method, resulting in the formation of highly stable quantum dot. The addition of trace amounts of PNP, the luminescence of the B,NQDs was significantly quenched, which was found to be linearly dependent on the PNP concentration in the range of 100pM to 6 μM. Further analysis of steady-state absorption and emission, along with photoluminescence decay dynamics, revealed the formation of both static and dynamic quenching complexes. Our simple fluorimetry-based sensor demonstrated an impressive limit of detection (LOD) of 9.08 nM, making it highly selective and sensitive for the detection of PNP. Additionally, the B,NQDs exhibited exceptional stability with respect to pH, UV exposure, salinity, and storage conditions. Finally, we successfully demonstrated the detection of PNP in real water systems and pesticides.

Probing energy transfer in luminescent CaMoO4:Tb3+ by steady state and decay dynamics

Polyvinylpyrrolidone functionalized CaMoO4:Tb3+ were synthesized hydrothermally. The formation of tetragonal phase CaMoO4:Tb3+ and morphology of nanoparticles are thoroughly studied with XRD, TEM and FT-IR spectroscopy. Nanophosphors show green emission of Tb3+ at 544 nm when excited at 290 nm due to MoO42− absorption. The energy transfer from the host MoO42− to the activator Tb3+ is occurred mainly through dipole-dipole interactions. The decay lifetime of MoO42− emission decreases from ∼13 to 1 μs with the increase in Tb3+ concentration indicating occurrence of energy transfer. This is further corroborated with the calculation of radiative and non-radiative decay rates. The quantum yield and CIE color chromaticity are also studied.

Enhanced Fluorescence Based on Slow Light Effect of ZIF-8 Photonic Crystals for Trace 2,4,6-Trinitrophenol Detection.

In response to growing concerns about public safety and environmental conservation, it is essential to develop a precise identification method for trace explosives. To improve the stability and detection sensitivity of perovskite quantum dots (PQDs) and address the issue of low porosity in traditional polymer-based photonic crystals (PhCs), this study proposed a PQD photoluminescence (PL) enhancement strategy based on the slow light effect of ZIF-8 PhCs for highly sensitive, selective, and convenient detection of 2,4,6-trinitrophenol (TNP). The slow light effect at the photonic band gap edge is the basis of amplifying the PL signal. PhCs were fabricated by the evaporation-induced self-assembly method. The diffraction wavelength overlapping the whole visible region was designed to match the emission wavelength of PQDs. Results showed that PhCs matching the PBG edge with PQDs' emission peak amplified the PL signal 11.3 times, significantly improving sensitivity for trace TNP detection with a limit as low as 2.52 nM. Moreover, there was a 13.3-fold enhancement of PQDs' fluorescence lifetime when the emission wavelength fell in the PBG range. The hydrophobic surface of ZIF-8 PhCs enhanced the PQDs' stability and moisture resistance. Furthermore, the selective quenching mechanism of TNP by the sensor was photoinduced electron transfer (PET) verified by DFT calculations and time-resolved PL decay dynamics measurements. This study demonstrated great potential for manipulating light emission enhancement by PhCs in developing efficient fluorescent sensors for trace environmental pollutant detection.

Decay Dynamics of a Single Spherical Domain in Near-Critical Phase-Separated Conditions.

Domain decay is at the heart of the so-called evaporation-condensation Ostwald-ripening regime of phase ordering kinetics, where the growth of large domains occurs at the expense of smaller ones, which are expected to "evaporate." We experimentally investigate such decay dynamics at the level of a single spherical domain picked from one phase in coexistence and brought into the other phase by an optomechanical approach, in a near-critical phase-separated binary liquid mixture. We observe that the decay dynamics is generally not compatible with the theoretically expected surface-tension decay laws for conserved order parameters. Using a mean-field description, we quantitatively explain this apparent disagreement by the gradient of solute concentrations induced by gravity close to a critical point. Finally, we determine the conditions for which buoyancy becomes negligible compared to capillarity and perform dedicated experiments that retrieve the predicted surface-tension induced decay exponent. The surface-tension driven decay dynamics of conserved order parameter systems in the presence and the absence of gravity, is thus established at the level of a single domain.

Ultrafast dynamics of exciton-polariton fluids at non-zero momenta

In this study, we have explored the ultrafast formation and decay dynamics of exciton-polariton fluids at non-zero momenta, non-resonantly excited by a small-spot femtosecond pump pulse in a ZnO microcavity. Using the femtosecond angle-resolved spectroscopic imaging technique, multidimensional dynamics in both the energy and momentum degrees of freedom have been obtained. Two distinct regions with different decay rate in the energy dimension and various decay-channels in the momentum dimension can be well-resolved. Theoretical simulations based on the generalized Gross–Pitaevskii equation can reach a qualitative agreement with the experimental observations, demonstrating the significance of the initial potential barrier induced by the pump pulse during the decay process. The finding of our study can provide additional insights into the fundamental understanding of exciton-polariton condensates, enabling further advancements for controlling the fluids and practical applications.

The addition of ascorbic acid improves the microbiological quality and shelf life of Atlantic mackerel (&lt;i&gt;Scomber scombrus&lt;/i&gt;) fillets stored in ice

Ascorbic acid is one of the most promising additives for improving fish shelf life, but studies on its antimicrobial activity during product storage are limited. In this experiment, we assessed the effect of ascorbic acid on the preservability of Atlantic mackerel (Scomber scombrus) fillets during storage in ice. Fillets were treated to reach an ascorbic acid concentration of 0.30 mg/g (T1) and 0.15 mg/g (T2). Samples were stored in ice at 0°C and analyzed at 0, 2, 7, 9, and 14 days for total viable count, specific spoilage organisms (SSOs), Pseudomonas spp., potentially histamine-producing bacteria (HPB), and Enterobacteriaceae. Growth curves were constructed using the DMfit tool of Combase, and the shelf life was estimated in relation to microbiological limits reported in the literature. Sensory evaluation was performed using a quality index method scheme. At 7 and 9 days of storage, treated samples exhibited bacterial counts from 0.5 to 1.7 Log CFU/g lower than controls, with a logarithmic reduction proportional to the additive concentration. The antimicrobial action appeared to diminish after 14 days. A consistent effect was observed for potentially HPB, with counts of 1.7 Log CFU/g lower in T1 samples compared to controls at 9 days. The moderate effect on SSOs limited the estimated shelf life, as the critical limit was reached after 7 days and 8.4 days (T1 and T2). Ascorbic acid positively impacted the microbiological characteristics of mackerel fillets. Further investigation into the decay dynamics of the additive in fish products during storage is advisable.