Decay Dynamics Research Articles

A High-Quality CdSe/CdS/ZnS Quantum-Dot-Based FRET Aptasensor for the Simultaneous Detection of Two Different Alzheimer's Disease Core Biomarkers.

The simultaneous detection of two different biomarkers for the point-of-care diagnosis of major diseases, such as Alzheimer's disease (AD), is greatly challenging. Due to the outstanding photoluminescence (PL) properties of quantum dots (QDs), a high-quality CdSe/CdS/ZnS QD-based fluorescence resonance energy transfer (FRET) aptasensor for simultaneously monitoring the amyloid-β oligomers (AβO) and tau protein was proposed. By engineering the interior inorganic structure and inorganic-organic interface, water-soluble dual-color CdSe/CdS/ZnS QDs with a near-unity PL quantum yield (>90%) and mono-exponential PL decay dynamics were generated. The π-π stacking and hydrogen bond interaction between the aptamer-functionalized dual-color QDs and gold nanorods@polydopamine (Au NRs@PDA) nanoparticles resulted in significant fluorescence quenching of the QDs through FRET. Upon the incorporation of the AβO and tau protein, the fluorescence recovery of the QDs-DNA/Au NRs@PDA assembly was attained, providing the possibility of simultaneously assaying the two types of AD core biomarkers. The lower detection limits of 50 pM for AβO and 20 pM for the tau protein could be ascribed to the distinguishable and robust fluorescence of QDs and broad spectral absorption of Au NRs@PDA. The sensing strategy serves as a viable platform for the simultaneously monitoring of the core biomarkers for AD and other major diseases.

Mesoscale connections and gene expression empower whole-brain modeling of α-synuclein spread, aggregation, and decay dynamics.

An emerging view regarding neurodegenerative diseases is that discreet seeding of misfolded proteins leads to widespread pathology. However, the mechanisms by which misfolded proteins seed distinct brain regions and cause differential whole-brain pathology remain elusive. We used whole-brain tissue clearing and high-resolution imaging to longitudinally map pathology in an α-synuclein pre-formed fibril injection model of Parkinson's disease. Cleared brains at different time points of disease progression were quantitatively segmented and registered to a standardized atlas, revealing distinct phases of spreading and decline. We then fit a computational model with parameters that represent α-synuclein pathology spreading, aggregation, decay, and gene expression pattern to this longitudinal dataset. Remarkably, our model can generalize to predicting α-synuclein spreading patterns from several distinct brain regions and can even estimate their origins. This model empowers mechanistic understanding and accurate prediction of disease progression, paving the way for the development and testing of therapeutic interventions.

Nonequilibrium plasma in water vapor

A kinetic model of a non-equilibrium water vapor plasma created by a nanosecond pulsed discharge at elevated temperatures and at low pressure is presented. The model includes equations for electron, vibrational and gas temperatures combined with equations for neutral, charged, electronically and vibrationally excited species. Simulation results are compared with the available experimental data and show good agreement in dynamics of the plasma decay and electron drift velocities. It is shown that the plasma decay in pure water vapor is controlled by the dissociative recombination. Under the conditions simulated, the concentration of electronically excited species is low, but we observe a formation of vibrationally excited species. A significant decrease in the electrical conductivity of water plasma with time, which depends on the level of initial ionization, is shown.

Probing the ultrafast dynamics of excitons in single semiconducting carbon nanotubes

Excitonic states govern the optical spectra of low-dimensional semiconductor nanomaterials and their dynamics are key for a wide range of applications, such as in solar energy harvesting and lighting. Semiconducting single-walled carbon nanotubes emerged as particularly rich model systems for one-dimensional nanomaterials and as such have been investigated intensively in the past. The exciton decay dynamics in nanotubes has been studied mainly by transient absorption and time-resolved photoluminescence spectroscopy. Since different transitions are monitored with these two techniques, developing a comprehensive model to reconcile different data sets, however, turned out to be a challenge and remarkably, a uniform description seems to remain elusive. In this work, we investigate the exciton decay dynamics in single carbon nanotubes using transient interferometric scattering and time-resolved photoluminescence microscopy with few-exciton detection sensitivity and formulate a unified microscopic model by combining unimolecular exciton decay and ultrafast exciton-exciton annihilation on a time-scale down to 200 fs.

Molecular insight into the polymorphism-dependent organic phosphorescence

Room temperature phosphorescence (RTP) in organic aggregates generally depends on the molecular conformation and packing, but the coupling between them presents a formidable challenge to uncovering the inherent mechanism in polymorphism-dependent RTP. Herein, organic polymorphs of DOS compounds (DOS-O and DOS-S), exhibiting different RTP lifetimes, were chosen as prototypes. By exploring the molecular and electronic structures, and the decay dynamics of T1 states for DOS polymorphs, we proposed that the decreased energy gap of T1 states caused by conformational variation governs the shortening of RTP lifetime from DOS-O to DOS-S. This is because it hugely accelerates the nonradiative decay rate of T1 → S0, in contrast to the negative contribution from the spin-orbit coupling and reorganization energy. This point was further demonstrated by the good consistency between theory and experiment in RTP lifetime.

Temperature-Dependent Decay of Quasi-Two-Dimensional Vortices across the BCS-BEC Crossover.

We systematically study the decay of quasi-two-dimensional vortices in an oblate strongly interacting Fermi gas over a wide interaction range and observe that, as the system temperature is lowered, the vortex lifetime increases in the Bose-Einstein condensate (BEC) regime but decreases at unitarity and in the Bardeen-Cooper-Schrieffer (BCS) regime. The observations can be qualitatively captured by a phenomenological model simply involving diffusion and two-body collisional loss, in which the vortex lifetime is mostly determined by the slower process of the two. In particular, the counterintuitive vortex decay in the BCS regime can be interpreted by considering the competition between the temperature dependence of the vortex annihilation rate and that of unpaired fermions. Our results suggest a competing mechanism for the complex vortex decay dynamics in the BCS-BEC crossover for the fermionic superfluids.

Modulating the Rise and Decay Dynamics of Upconversion Luminescence through Controlling Excitations

AbstractDifferent from organic dye/quantum dot possessing one luminescent center, upconversion luminescence (UCL) is actually a statistic of temporal behaviors of countless individual activators. Our experimental results have shown that the rise and decay dynamics of UCL is directly associated with the relative contribution of sensitizer‐to‐activator energy transfer and energy migration among sensitizers, which can be physically modulated by simply tuning the excitation laser. Therefore, dynamic UCL with record‐wide 20‐fold lifetime, ≈70‐fold red‐to‐green intensity ratio, and reversibly definable emission color is easily realized by just modulating the excitation laser. Moreover, this generally applicable strategy only requires a simplest‐possible UCL system whereas prevalent material engineering such as complicated composition design, sophisticated core–shell construction, or tedious chemical synthesis, is no longer needed.

Modulating the Rise and Decay Dynamics of Upconversion Luminescence through Controlling Excitations.

Different from organic dye/quantum dot possessing one luminescent center, upconversion luminescence (UCL) is actually a statistic of temporal behaviors of countless individual activators. Our experimental results have shown that the rise and decay dynamics of UCL is directly associated with the relative contribution of sensitizer-to-activator energy transfer and energy migration among sensitizers, which can be physically modulated by simply tuning the excitation laser. Therefore, dynamic UCL with record-wide 20-fold lifetime, ≈70-fold red-to-green intensity ratio, and reversibly definable emission color is easily realized by just modulating the excitation laser. Moreover, this generally applicable strategy only requires a simplest-possible UCL system whereas prevalent material engineering such as complicated composition design, sophisticated core-shell construction, or tedious chemical synthesis, is no longer needed.

A theoretical study on the impact of centrifugal potential and fragment identification in the decay of compound nuclei (ACN = 60&100)

Decay analysis of compound nuclei such as [Formula: see text] and [Formula: see text] formed in [Formula: see text]Ca and [Formula: see text]Ni reactions, respectively, is studied using two theoretical frameworks, dynamical cluster-decay model (DCM) and PACE4. To explore the decay dynamics in a relatively lighter mass region [Formula: see text], two more reactions are picked (i) [Formula: see text]Mg forming the [Formula: see text] compound nucleus, (ii) another one involving the odd mass projectile, [Formula: see text]. In DCM, the fusion excitation functions are calculated using sticking [Formula: see text] and nonsticking [Formula: see text] limits of the moment of inertia. For the chosen reactions, fusion cross-sections are equivalent to evaporation residue (ER) cross-sections [Formula: see text] as fission cross-sections are negligible. A lower magnitude of maximum angular momentum [Formula: see text] is obtained via the [Formula: see text] approach in comparison to the [Formula: see text] approach and the angular momentum obtained via the [Formula: see text] approach is closer to the experimental observations. The structure and magnitude of fragmentation potential and preformation probability [Formula: see text] depend on the choice of moment of inertia and the magnitude of angular momentum involved. Besides this, PACE4 is employed to address the fusion cross-section of chosen reactions. The most probable decay channel is identified using both DCM and PACE4 approaches.

Temporal dusty plasma afterglow: A review

In complex plasmas, dust particles are charged through their interactions with the electrons and ions of the surrounding plasma. In low-temperature laboratory plasmas, dust particles most commonly acquire a negative charge. In particular, in a laboratory glow-discharge plasma, the typical charge for a micrometer-size grain generally attains a few thousands of electronic charges. Under stable discharge conditions, this large negative charge is relatively well-characterized. However, for unsteady discharge conditions, the charge can differ and even fluctuate. In particular, when the power source of the discharge is turned off, the charged species of the plasma diffuse away and recombine into neutral species: this is a temporal afterglow. When dust particles are present inside a temporal plasma afterglow, the diffusion of charged species and the plasma decay dynamics are affected. Moreover, the dust particle charges also evolve during the afterglow period. In the late afterglow, dust particles are known to keep residual charges. The value of these residual charges strongly depends on the ambipolar-to-free diffusion transition. In addition, the presence of a constant electric field, causing ions to drift through the neutral gas, has a strong influence on the final dust particle residual charges, eventually leading to large positive residual charges. In this review article, the dynamics of temporal complex plasma afterglow are discussed. Experimental and theoretical results are presented. The basics of temporal afterglow modeling are also given.

Analysis of formation and decay of Ba*122,128 formed via Ni58,64+Ni64 reactions near the Coulomb barrier

The fusion mechanics of $^{58}\mathrm{Ni}+^{64}\mathrm{Ni}$ and $^{64}\mathrm{Ni} +^{64}\mathrm{Ni}$ reactions is analyzed by using the energy dependent Woods-Saxon potential (EDWSP) model and the subsequent decay dynamics of $^{122}\mathrm{Ba}^{*}$ and $^{128}\mathrm{Ba}^{*}$ isotopes formed in these fusion channels is examined via the dynamical cluster-decay model (DCM). In the EDWSP model, the energy dependent nature of the Woods-Saxon potential causes modifications in the profile of the fusion barrier between fusing nuclei. Such barrier modifications lead to the lowering of the effective fusion barrier of the colliding nuclei. Hence, EDWSP outcomes satisfactorily describe the energy dependence of fusion cross sections of the chosen reactions in near- and sub-barrier energy regions. Following this, the fragmentation of compound nuclei $^{122}\mathrm{Ba}^{*}$ and $^{128}\mathrm{Ba}^{*}$ formed using the above-mentioned reactions is investigated by using the collective clusterization approach of DCM. The calculations are done for quadrupole $({\ensuremath{\beta}}_{2})$ choice of fragmentation with hot configurations having optimized orientations. The evaporation residues' cross-section data lying within beam energy $({E}_{\mathrm{beam}})$ = 171--220 MeV are nicely addressed. The comparative analysis of decaying $^{122}\mathrm{Ba}^{*}$ and $^{128}\mathrm{Ba}^{*}$ nuclei is worked out in terms of fragmentation potential and preformation probability, along with the investigation of barrier characteristics.

Significant impact of deprotonated status on the photoisomerization dynamics of bacteriophytochrome chromophore

We report that the photoinduced dynamics of the phytochrome chromophore is strongly dependent on the protonation/deprotonation states of the pyrrole ring. The on-the-fly surface hopping dynamics simulations were performed to study the photoisomerization of different protonation/deprotonation phytochrome chromophore models. The simulation results indicate that the deprotonations at the pyrrole rings significantly modify the photoinduced nonadiabatic dynamics, leading to distinctive population decay dynamics and different reaction channels. Such feature can be well explained by the formation of the different hydrogen bond network patterns. Therefore, the proper understanding of the photoisomerization mechanism of phytochrome chromophore must take the hydrogen bond network into account. This work provides the new insights into the photobiological functions of phytochrome chromophore and suggests the possible ideas to control of its photoconversion processes for further rational engineering in optical applications.

One-Step Hydrothermal Synthesis of Highly Fluorescent MoS2 Quantum Dots for Lead Ion Detection in Aqueous Solutions.

Lead ions in water are harmful to human health and ecosystems because of their high toxicity and nondegradability. It is important to explore effective fluorescence probes for Pb2+ detection. In this work, surface-functionalized molybdenum disulfide quantum dots (MoS2 QDs) were prepared using a hydrothermal method, and ammonium tetrathiomolybdate and glutathione were used as precursors. The photoluminescence quantum yield of MoS2 QDs can be improved to 20.4%, which is higher than that for MoS2 QDs reported in current research. The as-prepared MoS2 QDs demonstrate high selectivity and sensitivity for Pb2+ ions, and the limit of detection is 0.056 μM. The photoluminescence decay dynamics for MoS2 QDs in the presence of Pb2+ ions in different concentrations indicate that the fluorescence quenching originated from nonradiative electron transfer from excited MoS2 QDs to the Pb2+ ion. The prepared MoS2 QDs have great prospect and are expected to become a good method for lead ion detection.

Charge Carrier Dynamics of Organic Cation-Treated Perovskites Probed with Time-Resolved Microwave Conductivity

Metal halide perovskites have emerged as a set of promising optoelectronic materials benefiting from their outstanding optoelectronic properties and unprecedented success in photovoltaics. Recent studies have suggested that mixing lower-dimensional A-site cations within perovskites helps mitigate this environmental and phase instability for 3D perovskites. However, the charge carrier transport properties in mixed 2D/3D perovskites are still not fully understood. In this work, charge carrier mobilities and recombination rate constants in perovskite thin films were analyzed with transient time-resolved microwave conductivity and time-resolved photoluminescence. It was found that upon large-cation treatment of 3D perovskites, charge carrier transport and radiative recombination efficiency were enhanced by the passivation of surface defects, which is evidenced by the decay dynamics of charge carriers.

Computational studies on the excited state decay rates in aggregates of two‐coordinate Cu (I) complexes: Thermally Activated Delayed Fluorescence and Aggregation Induced Emis

AbstractTwo‐coordinate Cu (I) complexes have attracted great interest recently because of the rich photophysical property in solid state, including the aggregation‐induced thermal activated delayed fluorescence. Here, we summarize our theoretical investigations on the excited state structure and decay dynamics for the two‐coordinate Cu (I) complexes in solution phase and solid state by the thermal vibration correlation function rate formalism we developed earlier coupled with time‐dependent density‐functional theory within polarizable continuum model and hybrid quantum and molecular mechanics. First, for the CAACCu (I)Cl complex, we found that the nature of the excited state undergoes a change from metal‐to‐ligand charge transfer (MLCT) in solution to hybrid halogen‐to‐ligand charge transfer and MLCT in solid state. The bending vibrations of the CCuCl and CuCN bonds are restricted in aggregates, reducing the non‐radiative decay rate to cause strong solid‐state fluorescence. Second, for CAACCu (I)Cz, we found that both intersystem crossing (ISC) and reverse intersystem crossing (rISC) are enhanced by 2–4 orders of magnitudes upon aggregation, leading to highly efficient thermally activated delayed fluorescence (TADF). The enhanced ISC and rISC rates can be attributed to the increase of the metal proportion in the frontier molecular orbitals, leading to an enhanced spin−orbit coupling between S1 and T1. The reaction barriers for ISC and rISC are much lower in solution than that in aggregate phase resulting in a decrease in energy gap and an increase in the relative reorganization energy through bending the angle ∠C − Cu − N for T1. Our theoretical studies provide a clear rationalization for the highly efficient solid‐state luminescence character of two‐coordinate Cu (I) complexes and may clarify the ongoing dispute on the understanding of the high TADF quantum efficiency.

Accounting for non-rainfall moisture and temperature improves litter decay model performance in a fog-dominated dryland system

Abstract. Historically, ecosystem models have treated rainfall as the primary moisture source driving litter decomposition. In many arid and semi-arid lands, however, non-rainfall moisture (fog, dew, and water vapor) plays a more important role in supporting microbial activity and carbon turnover. To date though, we lack a robust approach for modeling the role of non-rainfall moisture in litter decomposition. We developed a series of simple litter decay models with different moisture sensitivity and temperature sensitivity functions to explicitly represent the role of non-rainfall moisture in the litter decay process. To evaluate model performance, we conducted a 30-month litter decomposition study at 6 sites along a fog and dew gradient in the Namib desert, spanning almost an eightfold difference in non-rainfall moisture frequency. Litter decay rates in the field correlated with fog and dew frequencies but not with rainfall. Including either temperature or non-rainfall moisture sensitivity functions improved model performance, but the combination of temperature and moisture sensitivity together provided more realistic estimates of litter decomposition than relying on either alone. Model performance was similar regardless of whether we used continuous moisture sensitivity functions based on relative humidity or a simple binary function based on the presence of moisture, although a Gaussian temperature sensitivity outperformed a monotonically increasing Q10 temperature function. We demonstrate that explicitly modeling non-rainfall moisture and temperature together is necessary to accurately capture litter decay dynamics in a fog-affected dryland system and provide suggestions for how to incorporate non-rainfall moisture into existing Earth system models.

Synthesis of Weakly Confined, Cube-Shaped, and Monodisperse Cadmium Chalcogenide Nanocrystals with Unexpected Photophysical Properties.

Zinc-blende CdSe, CdS, and CdSe/CdS core/shell nanocrystals with a structure-matched shape (cube-shaped, edge length ≤30 nm) are synthesized via a universal scheme. With the edge length up to five times larger than exciton diameter of the bulk semiconductors, the nanocrystals exhibit novel properties in the weakly confined size regime, such as near-unity single exciton and biexciton photoluminescence (PL) quantum yields, single-nanocrystal PL nonblinking, mixed PL decay dynamics of exciton and free carriers with sub-microsecond monoexponential decay lifetime, and stable yet extremely narrow PL full width at half maximum (FWHM < 0.1 meV) at 1.8 K. Their monodisperse edge length, shape, and facet structure enable demonstration of unexpected yet size-dependent PL properties at room temperature, including unusually broad and abnormally size-dependent PL FWHM (∼100 meV), nonmonotonic size dependence of PL peak energy, and dual-peak single-exciton PL. Calculations suggest that these unusual properties should be originated from the band-edge electron/hole states of the dynamic-exciton, whose exciton binding energy is too small to hold the photogenerated electron-hole pair as a bonded Wannier exciton in a weakly confined nanocrystal.

Nucleon–nucleon correlations in the extreme oxygen isotopes

There has been an upsurge of interest in two-nucleon decays thanks to the studies of nucleon–nucleon correlations. In our previous work (2021 Phys. Rev. Lett. 126 142501), based on a novel time-dependent three-body approach, we demonstrated that the energy and angular correlations of the emitted nucleons can shed light on the structure of nucleonic pairs formed inside the nucleus. In this work, we apply the new framework to study the decay dynamics and properties of some extreme proton-rich and neutron-rich oxygen isotopes, including two-proton (2p) decays of 11,12O and two-neutron (2n) decay of 26O. Here we show that the low-ℓ components of 11,12O wave functions, which are affected by continuum and configuration-interaction effects, strongly impact decay dynamics and asymptotic correlations. In the calculated wave functions of 11,12O, diproton and cigarlike structures merge together during the tunneling process and the resulting energy and angular correlations are very consistent with the experimental data. The asymptotic correlations of the 2n decay of 26O dramatically change as the 2n decay energy approaches the zero-energy threshold. The small reported value of Q 2n suggests that the 2n decay of this nucleus can be understood in terms of the universal phase-space limit.

Incorporating Lindblad decay dynamics into mixed quantum-classical simulations.

We derive the L-mean-field Ehrenfest (MFE) method to incorporate Lindblad jump operator dynamics into the MFE approach. We map the density matrix evolution of Lindblad dynamics onto pure state coefficients using trajectory averages. We use simple assumptions to construct the L-MFE method that satisfies this exact mapping. This establishes a method that uses independent trajectories that exactly reproduce Lindblad decay dynamics using a wavefunction description, with deterministic changes of the magnitudes of the quantum expansion coefficients, while only adding on a stochastic phase. We further demonstrate that when including nuclei in the Ehrenfest dynamics, the L-MFE method gives semi-quantitatively accurate results, with the accuracy limited by the accuracy of the approximations present in the semiclassical MFE approach. This work provides a general framework to incorporate Lindblad dynamics into semiclassical or mixed quantum-classical simulations.

Probing the Carrier Dynamics of Polymer Composites with Single and Hybrid Carbon Nanotube Fillers for Improved Thermoelectric Performance

The incorporation of carbon nanotubes (CNTs) within polymer hosts offers a great platform for the development of advanced thermoelectric (TE) composite materials. Over the years, several CNT/polymer composite formulations have been investigated on an effort to maximize the TE performance. Meanwhile, several studies focused on the decay dynamics of the charged excitons within CNTs itself and therefrom derived structures, aiming to investigate the lifetimes and the corresponding recombination processes of free charge carriers. The latter physical phenomena play a crucial role in the performance of various types of energy converting and scavenging materials. Nevertheless, up to this date, there is no systematic study on the combination of TE parameters and the critical charge carrier dynamics within CNT containing TE polymer composites. Herein, a variety of composites with single and hybrid CNT fillers based on polycarbonate (PC) and polyether ether ketone (PEEK) polymer matrices were prepared by melt-mixing in small scale. At the same loading, the addition of single fillers in PC results in higher Seebeck coefficients and similar conductivities when compared to the use of hybrid filler systems. In contrast, with hybrid filler systems in PEEK composites, higher power factors could be reached than in single filler composites. Moreover, the PC-based composites are studied using ultrafast laser time-resolved transient absorption spectroscopy (TAS), for the investigation of the exciton lifetimes and the physical origins of free charge carrier transport within the TE films. The findings of this study reveal interesting links between the TE parameters and the obtained charge carrier dynamics.