Characteristic Decay Time Research Articles

Decadal-scale decay of landslide-derived fluvial suspended sediment after Typhoon Morakot

Abstract. Landslides influence fluvial suspended sediment transport by changing sediment supply and grain size, which alter suspended sediment concentrations and fluxes for a period of time after landsliding. To investigate the duration and scale of altered suspended sediment transport due to landsliding, we analyzed suspended sediment concentration and water discharge measurements at 87 gauging stations across Taiwan over an 11-year period after Typhoon Morakot, which generated nearly 20 000 landslides in 2009. At each gauging station, we computed annual rating curves to quantify changes over time in the sensitivity of suspended sediment concentrations to water discharge. Among the 40 stations in basins that were impacted by landsliding, the discharge-normalized rating curve coefficient ã was higher than that before Morakot by a factor of 5.1±1.1 (mean ± standard error) in 2010, the first year after Morakot. The rating curve exponent b did not decrease at most stations until a year later (2011), when the average b value was lower than that before Morakot by 0.25±0.05. Across the compilation of gauging stations, post-Morakot changes in discharge-normalized sediment concentration (ã) were positively correlated with landslide intensity for 7 years after Morakot, while post-Morakot changes in the exponent of the discharge–concentration relationship (b) were negatively correlated with landslide intensity from 2011 to 2014. This reflects a tendency for larger changes in ã and b to occur in basins with more intense landsliding. At 26 of these 40 stations, elevated values of ã declined after the initial post-Morakot peak, consistent with a gradual return to pre-Morakot suspended sediment transport conditions. Exponential regressions to these ã values reveal a median characteristic decay time of 8.8 years (interquartile range: 5.7–14.8 years). Values of ã increased more and declined faster in basins with more intense landsliding, with a mean characteristic decay time of 6 years in the basins hit hardest by landsliding. Furthermore, changes in ã and b tended to be larger in basins with more intense landsliding. At stations that were not impacted or only minimally impacted by landsliding, neither ã nor b exhibited systematic responses to Morakot. To quantify the effect of landsliding on sediment discharge, we compared the measured sediment discharges after Morakot to the hypothetical sediment discharges that would have occurred if Morakot had induced no landslides, calculated by applying each station's pre-Morakot rating curve to its post-Morakot water discharge history. This analysis suggests that Morakot-induced landsliding increased sediment discharge by as much as > 10-fold in some basins in the 1–2 years after Morakot. Together, these results indicate that the influence of Morakot-induced landsliding on rating curves was large shortly after Morakot but diminished in less than a decade in most of the study rivers and will be imperceptible in another few decades in all of the study rivers. To the extent that these results are applicable to other landscapes, this suggests that periods of elevated sediment transport efficiency after landsliding should persist for years to decades, even if the landslide deposits persist for centuries to millennia.

Transition from decaying to decayless kink oscillations of solar coronal loops

ABSTRACT The transition of an impulsively excited kink oscillation of a solar coronal loop to an oscillation with a stationary amplitude, i.e. the damping pattern, is determined using the low-dimensional self-oscillation model. In the model, the decayless kink oscillations are sustained by the interaction of the oscillating loop with an external quasi-steady flow. The analytical solution is based on the assumption that the combined effect of the effective dissipation, for example, by resonant absorption, and interaction with an external flow, is weak. The effect is characterized by a dimensionless coupling parameter. The damping pattern is found to depend upon the initial amplitude and the coupling parameter. The approximate expression shows a good agreement with a numerical solution of the self-oscillation equation. The plausibility of the established damping pattern is demonstrated by an observational example. Notably, the damping pattern is not exponential, and the characteristic decay time is different from the time determined by the traditionally used exponential damping fit. Implications of this finding for seismology of the solar coronal plasmas are discussed. In particular, it is suggested that a very rapid, in less than the oscillation period, decay of the oscillation to the stationary level, achieved for larger values of the coupling parameter, can explain the relative rareness of the kink oscillation events.

Methods for comparing theoretical models parameterized with field data using biological criteria and Sobol analysis

Prey–predator models are frequently developed to investigate trophic webs and to predict the population dynamics of prey and predators. However, the parameters of these models are often implemented without empirical data and may even be chosen arbitrarily. Commonly, only a few parameters are tested regarding their sensitivity and it is rare to read about the comparison between different prey–predator models (i.e. predation function structure). Here, we propose a method to compare four prey–predator models designed for two populations. We then apply this method to select the more biologically plausible one to model a simplified agricultural trophic system, including one predator compartment (the red fox Vulpes vulpes) and one prey group compartment (small mammals). These models are based on four Holling functional responses for the predation interaction and take the prey intrinsic growth rate into account through a Verhulst logistic function. Most parameters’ values (like attack rates or growth rates) were calculated from field data or based on literature review. We then used Sobol indices to conduct parameter exploration around mean parameter values to investigate and compare the model dynamics responses. Our first results showed that under our assumptions, the two most relevant models for our case study are the saturated Holling I and II models. We were also able to discriminate that among the 6 scaled parameters that vary, the model outputs are particularly sensitive to four of them (κ: saturation rate of the environment, Tr1: characteristic intrinsic decay time of the predators, Tc: characteristic growth time of the predator via the predation on the prey and λ: saturation rate of a predator’s stomach per time unit) and much less sensitive to two others (Tr2: characteristic intrinsic growth time of the prey and Ta: characteristic decay time of the prey due to the predation). These first encouraging results open the way for the next step, which will be to adapt this model construction to more complex prey–predator systems, with several predator and/or several prey compartments.

Signatures of Polaron Dynamics in Photoexcited MAPbBr3 by Infrared Spectroscopy.

Hybrid organic-inorganic perovskites (HOIPs) have attracted considerable attention in the past years as photoactive materials for low-cost, high-performance photovoltaics. Polaron formation through electron-phonon coupling has been recognized as the leading mechanism governing charge carrier transport and recombination in HOIPs. In this work, two types of MAPbBr3 film samples deposited on different substrates (transparent insulating SrTiO3 and a heterostructure mimicking a functioning photovoltaic cell) were photoexcited with above-bandgap radiation at 450 nm, and the effects of illumination on the sample were analyzed in the infrared region. The infrared absorbance detected at different powers of the photoexciting laser allowed us to obtain an estimate of the characteristic decay time of photoexcited polaron population of the order of 100-1000 ns. When focusing on the absorption features of the MA molecular cation in the region of the NH stretching modes, we observed the influence of hydrogen bonding and the effect of the polaron dynamics on the cation reorientation.

Interconfigurational d-f luminescence of Pr3+ ions in praseodymium doped Li6Y(BO3)3 single crystals

Luminescence properties of undoped Li6Y(BO3)3 (LYB) crystals grown by the Bridgman method as well as undoped and praseodymium doped LYB crystals grown by the Czochralski method were studied under excitation by ultraviolet light, synchrotron radiation and electron beam in the temperature region of 5–300 K. The emission bands peaking at 4.8, 3.76 and 2.95 eV were found in undoped Czochralski-grown crystals, while the band at 3.34 eV was dominant in the Bridgman-grown crystals. These bands are presumably ascribed to excitons localized at regular and defect-perturbed lattice sites. Intense emission bands peaking at 4.75, 4.50, 4.17 and 3.98 eV were discovered in Pr doped crystals at low temperatures and related to the interconfigurational 4f15d1 → 4f2 radiative transitions in Pr3+ ions. The structure of the emission spectrum is shown to be determined by the 3H4, 3H5, 3H6, 3F2, 3F3, 3F4 terms of the Pr3+ ion. The characteristic decay time of the 4f15d1 → 4f2 emission is τ = 24 ns at low temperatures, however, it shortens to 9 ns by room temperature due to a strong thermal quenching. The study of glow curves and spectra of thermostimulated luminescence in Li6Y(BO3)3:Pr crystal irradiated by 10-keV electron beam shows that Pr3+ ions do not participate in an electron-hole recombination process.

Influence of the Bismuth Content on the Optical Properties and Photoluminescence Decay Time in GaSbBi Films.

We report the optical properties of GaSbBi layers grown on GaSb (100) substrates with different bismuth contents of 5.8 and 8.0% Bi. Fourier-transform photoluminescence spectra were determined to identify the band gaps of the studied materials. Further temperature- and power-dependent photoluminescence measurements indicated the presence of localized states connected to bismuth clustering. Finally, time-resolved photoluminescence measurements based on single-photon counting allowed the determination of characteristic photoluminescence decay time constants. Because of the increasing bismuth content and clustering effects, an increase in the time constant was observed.

Evaluation of the effectiveness of energetic thermal electrons on the excitation of the ionospheric red 6300 Å airglow

In this paper we use previously calculated ionosphere electron temperatures Te in order to estimate the 6300 Å (red) airglow intensity enhancements attributed to thermal electrons from the tail of a Maxwellian electron distribution of sufficiently increased electron temperature. Then, we compare our results with the relevant observed measurements and we comment on the quality of the comparison and the possible causes of the differences. We also calculate the airglow intensity characteristic rise and decay times and compare them to the experimental ones, and we investigate the origin of the electrons which excite the red airglow. In the end, we assess the departure of the ionosphere electron energy distribution from a purely Maxwellian one, and the role of the electron elastic and inelastic collisions with the other components of the ionospheric F-region.

Current mode of photomultiplier tube operation for the detection of the kinetics of small optical signals

Subject of study. The possibility of using the nonlinear current mode of operation of a photomultiplier tube for measurements of luminescence kinetics was investigated. Aim of study. This study aimed to validate the possibility of using the nonlinear current mode of operation of a photomultiplier tube to determine the kinetic properties of small luminescence signals of condensed media, including the signals that cannot be detected in a linear current mode. Method. The signal arriving at a high-impedance (1 MΩ) input of a digital oscilloscope from a photomultiplier tube via a coaxial cable was measured. This signal is a convolution of a photocurrent pulse with a kinetic instrument function determined by the discharge of capacitance in the measurement circuit of the photomultiplier tube. The bandwidth of the circuit was determined by the lowest frequency of its elements instead of the characteristic time of the instrument function. The real photocurrent signal was reconstructed by the deconvolution of the digital convoluted array. The pulsed cathodoluminescence method was used to detect the kinetics. Main results. A method for measuring the kinetics of small optical signals in the current mode of operation of a photomultiplier tube connected to a high-impedance input of a digital oscilloscope was presented. The results of using this method to measure the kinetics of pulsed cathodoluminescence of impurity and intrinsic centers in ceramic and monocrystalline samples of yttrium aluminum garnet were presented. The direct determination of characteristic decay times by approximating the convoluted curves without deconvolution was demonstrated for an exponential luminescence decay profile. Practical significance. The proposed method for the characteristic time detection of luminescence kinetics enables comprehensive analysis of luminescence that can be applied in various sectors of the national economy.

Ультранизкочастотные осцилляции интенсивности люминесценции полимерной мембраны в водных растворах солей

The paper studies luminescence from the Nafion polymer membrane surface at its swelling in the isotonic aqueous solutions and bi-distilled water using the experimental photo luminescent spectroscopy. Liquid samples were preliminarily treated with the electric pulses with duration of 1 µs and amplitude of 0.1 V using antenna in the form of a flat capacitor. Experiments in photo luminescent spectroscopy were carried out 20 min after the electric pulse treatment. Typical luminescence intensity dependence on the membrane swelling time could be represented as the exponentially decreasing function. Characteristic decay time of the corresponding functions and stationary level of the membrane luminescence intensity depend on the electrical pulses repetition rate. The obtained dependencies could well be reproduced. However, dependence of the luminescence intensity at certain pulse repetition rates appears to be a random function, and the reproducibility is missing. It could be assumed that these stochastic effects are associated with exposure to random external force of the electromagnetic nature acting on the polymer membrane during swelling. Low-frequency pulsations of neutron stars or white dwarfs are the source of this random force according to the authors of the work. This effect is associated with depolarization during the low-frequency electromagnetic field scattering caused by the neutron stars pulsation. Depolarization effect arises due to scattering on long-living anisotropic clusters of nano-bubbles, which, in turn, are becoming anisotropic in the external field of a flat capacitor. Depolarized scattered radiation causes stochastic oscillations of the polymer fibers unwound into the bulk liquid. In this case, luminescence should also acquire the stochastic character taking into account the effect of resonant luminescence energy transfer from a donor to the luminescence acceptor

Dual‐Gate GaAs‐Nanowire FET for Room Temperature Charge‐Qubit Operation: A NEGF Approach

AbstractThe performance of dual‐gate GaAs‐nanowire field‐effect‐transistor (FET) is investigated as a charge‐qubit device operating at room temperature. In compatibility with the state‐of‐the‐art classical bit technology, it is shown that the single gate of a nanowire FET can be replaced by two localized gates to achieve such charge‐qubit operation. On application of relevant biases to the localized gates, two voltage tunable quantum dots are created within the nanowire channel with electrostatically controlled single‐state‐occupancy and interdot coupling leading to charge‐qubit operation at room temperature. The associated electron transport is theoretically modeled on the basis of nonequilibrium Green's function formalism. The “initialization” and “manipulation” for qubit operation are performed by applying suitable gate voltages, whereas the “measurement” is executed by applying a small drain bias to obtain a pulse current of ≈pA order. A ≈25 MHz frequency of coherent oscillation is observed for the qubit and a characteristic decay time of ≈ 70 ns is achieved. The results suggest that such dual gate nanowire FET is a promising architecture for charge‐qubit operation at room temperature.

Composition of resolvents enhanced by random sweeping for large-scale structures in turbulent channel flows

Composite sweeping-enhanced resolvents, referred to as the ${\boldsymbol {R}}_s^2$ model, are proposed to predict the space–time statistics of large-scale structures in turbulent channel flows. This model incorporates two key mechanisms: (i) eddy damping is introduced to represent random sweeping decorrelation caused by nonlinear forcing, leading to a sweeping-enhanced resolvent ${{\boldsymbol {R}}_s}$ ; and (ii) the sweeping-enhanced resolvent ${{\boldsymbol {R}}_s}$ is composited into its iterations ${\boldsymbol {R}}_s^2$ to yield non-zero Taylor time microscales. The resulting ${\boldsymbol {R}}_s^2$ model can correctly predict the frequency spectra and two-point cross-spectra of large-scale structures. This model is compared numerically with eddy-viscosity-enhanced resolvent models. The latter are designed to represent energy transfer instead for time decorrelation, and thus underpredict the characteristic decay time scales. The ${\boldsymbol {R}}_s^2$ model correctly yields the characteristic decay time scales in turbulent channel flows.

Radiation resistance of praseodymium-doped aluminum lithium fluorophosphate scintillator glasses for laser fusion experiments

We report the gamma (γ)-ray radiation resistance of praseodymium (Pr3+)-doped aluminum lithium fluorophosphate scintillator glasses. For its assessment as a scintillator material for laser fusion experiments, a 20Al(PO3)3-80LiF-PrF3 (Pr3+-doped APLF) glass was irradiated with γ-rays from a cobalt-60 (60Co) source resulting in an absorbed dose of 5.2 kGy. Although γ-ray-irradiation results in increased absorption due to phosphorus-oxygen hole centers (POHCs) and PO3 2− electron centers (PO3 ECs), these radiation-induced defects do not modify the glass emission as both non-irradiated and γ-ray-irradiated glasses exhibit similar emission spectra and decay times under optical and X-ray excitation. The emission peaks observed also correspond to the different interconfigurational 4f5d → 4f2 and intraconfigurational 4f2 transitions of Pr3+ ions which are neither oxidized nor reduced by irradiation. Our results show that Pr3+-doped APLF glass still maintains its characteristic fast decay time and that γ-ray irradiation does not affect the glass scintillation mechanisms.

Universal Matsubara time decay of quantum autocorrelations for Boltzmann particles.

The general properties of time dependent autocorrelations in many-body quantum systems are here analyzed at thermodynamic equilibrium in the Boltzmann canonical ensemble at temperature T, by means of the exponential expansion theory (EET). It is shown that the Kubo-Martin-Schwinger (KMS) symmetry applied to the exponential expansion of the correlation leads to the existence of two different sets of decay modes (channels) here indicated as "Matsubara modes" and "system modes," respectively. The Matsubara modes are a series of pure decay channels with time constants representing a direct action of the thermostat upon the correlation, with a characteristic principal decay time τ_{1}=ℏ/(2πk_{B}T), where ℏ and k_{B} are the Planck and Boltzmann constants, and T is the temperature. Moreover, the KMS condition implies that the amplitudes pertaining to the even and odd contribution of the system modes to the quantum correlation are not independent. These two properties are quantum mechanical in nature and "universal," in the sense that they are present for any autocorrelation of a quantum system at equilibrium at a temperature T. The Matsubara modes' contribution to the time behavior of a quantum correlation is limited to times of the order of τ_{1}, which however can be comparable with some of the characteristic decay times of the system modes. In addition, since the parameters representing the overall time behavior of the quantum correlation can be given in terms of the parameters of its Kubo transform, the EET representation turns out to be useful in calculations exploiting the outputs of some widespread quantum simulation methods. A discussion of the properties of these relations is described in detail with numerical examples. The case of the velocity autocorrelation function of para hydrogen at low temperature is also reported as a final example for a real system.

Stability of nonsteroidal anti-inflammatory drugs in contaminated fingermarks probed by Raman Spectroscopy: Effect of temperature and time since deposition

For over a decade, chemical analysis of fingermarks (FMs), with particular reference to “touch chemistry,” has offered additional intelligence to the forensics community. Therefore, understanding the FM degradation trends in the presence of exogenous contaminants is vital. The current study aimed to investigate the underlying changes in drugs in contaminated FMs upon exposure to different temperatures and times since deposition using Raman spectroscopy. For this purpose, five non-steroidal anti-inflammatory drugs (NSAIDs) were used to produce contaminated FMs, and their change at various temperatures and times was studied. We found that the Raman signal of aspirin, diclofenac, and ibuprofen in contaminated FMs were significantly reduced at high temperatures, whereas naproxen and ketoprofen were more stable at the studied temperatures. Furthermore, the chemical/physical changes of these drugs in FM samples were monitored for 40 days post-deposition. The Raman spectra of the FM contaminated with aspirin exhibited monotonic changes over time, whereas the diclofenac-, ibuprofen-, ketoprofen-, and naproxen-contaminated FMs showed little change. Additionally, the intensity of the Raman bands assigned to individual drugs showed a monoexponential decrease with time since FM deposition, and the characteristic decay time of each drug varied between 5 and 600 h. The present study advances the use of Raman spectroscopy to study the stability of drugs in FM samples exposed to high temperatures and aged up to 40 days.

Stepwise development of atmospheric pressure plasma jet driven by bursts of high-voltage nanosecond pulses at multi-tens MHz

This study employs the bursts of high-voltage nanosecond pulses at multi-tens MHz to drive the helium atmospheric pressure plasma jet. Such bursts are obtained by modulating a high-voltage nanosecond pulse based on the wave reflections in a coaxial cable. The development processes and mechanisms of the plasma jet are analyzed in detail based on the discharge waveforms, discharge images, gas temperature, electron density, and axial electric field. Because the time interval between adjacent pulses is much shorter than the characteristic plasma decay time, the discharge channel driven by the first pulse still has high residual electron density and conductivity when the second pulse arrives. The first discharge channel serves as an extension of the high-voltage electrode. In this case, the second discharge starts at the end of the first discharge channel and continues to propagate forward. Driven by the bursts of high-voltage nanosecond pulses, the stepwise propagation of a guided streamer along the plasma jet is observed. The characteristic of the stepwise development of the guided streamer is stable and repeatable under the same condition and does not change at different helium flow rates if the flow is laminar. Reducing the cable length results in a higher equivalent pulse frequency in the bursts and significantly increases the plasma jet length. However, an excessively high frequency will cause a rise in gas temperature and pressure fluctuation in helium flow, resulting in a reduction in the length of the laminar region and an unstable discharge.

Photophysical properties of methylene blue in aqueous solution sprayed onto biological surfaces

The paper presents a set of experiments revealing photophysical processes associated with methylene blue assisted photodynamic inactivation of pathogens on different surfaces, both inorganic (glass) and organic (superficial fascial flaps of chicken and fish and mushroom cap peel). The experiments were performed in normoxic and hyperoxic conditions. The characteristic times of singlet oxygen generation and degradation on the surfaces were evaluated from the analysis of time-resolved signals of singlet oxygen phosphorescence. The photobleaching kinetics of methylene blue on the surfaces were found to be significantly different and dependant on solution oxygenation. The characteristic decay times varied from dozens of seconds for glass to dozens of minutes for fascial flaps and mushroom peel. The interpretation of the experimental results obtained was done on the basis of a set of master equations describing photosensitizer-assisted singlet oxygen generation and photosensitizer photobleaching. The results obtained on methylene blue photodynamics and conclusions made were compared with results of similar experiments performed earlier with Radachlorin photosensitizer.

Sharp luminescence system in titanium dioxide with zero-phonon transition at 1.573 eV

In this paper, we discuss near-IR steady-state and time-resolved low-temperature (5 K) luminescence of crystalline titanium dioxide (TiO2) powders with different particle sizes. Upon optical excitation with quantum energy close to 3.1 eV, the near-IR luminescence of all the powders reveals a very similar characteristic spectrum, which includes a narrow 1.573 eV line, a set of wider peaks in 1.565–1.545 eV range, and a broad band at ∼1.42 eV. The spectrum remains unchanged when using different excitation quanta, thus indicating that all components are governed by the same luminescence system. It is also confirmed by identic two-exponential luminescence decays with characteristic decay times 70 μs and 400 μs observed for all parts of the spectrum. The properties of the luminescent system are not sensitive to the crystallite size reduction to 10 nm, and its intensity sharply increases after annealing converting the anatase phase into rutile. A comparison of the spectrum with TiO2 phonon density of states indicates that 1.573 eV peak is a zero-phonon transition, and 1.545–1.565 eV structure is due to interaction with bulk phonons of rutile phase. The band at 1.42 eV seems to be due to non-adiabatic electron-phonon coupling. The data obtained clearly indicates that the luminescent system is governed by inner shells of transition elements located in rutile lattice. This transition element can be vanadium as it follows from ICP-MS data and theoretical modeling. The detected luminescent system provides a convenient optical marker of TiO2, including nanoform, and thus can be useful for some applications related to medicine, biology, as well as the food industry.

Thin film rheology via focused laser spike thermocapillary dewetting

Focused laser spike (FLaSk) dewetting employs a localized heat source to create thermocapillary-induced trench-ridge morphologies. Using a universal heating substrate coupled with optical microscopy, we have studied the dewetted ridge feature for several distinct thin films of glass-forming materials. The evolution of the ridge’s radius over time can be modeled to derive a maximum dewetted radius and a characteristic decay time. The decay time shows an Arrhenius behavior when compared to the mean melt pool temperature, leading to a characteristic activation energy. An effective viscosity can also be defined. These descriptors demonstrate FLaSk’s potential for rapid metrology.

Microscopic Dynamics and Viscoelasticity of Vitrimers

We implement a hybrid molecular dynamics/Monte Carlo simulation to study the microscopic dynamics and the macroscopic rheology of vitrimers with a fast bond exchange rate. We show that the linear viscoelastic properties and mean squared displacement of the vitrimers collapse onto master curves by applying the same shift factors that follow the Williams–Landel–Ferry equation at low temperatures and Arrhenius-like behavior at high temperatures. The linkage between the microscopic dynamics and the linear rheology of vitrimers is established using the generalized Stokes–Einstein relationship, which efficiently extends the timescale of simulations and predicts the viscoelasticity. The values of the shift factors are related to the characteristic decay time of the intermediate scattering function, which is accessible in scattering experiments. The same results hold in the case of an all-atom model of an ionic liquid. Our methodology provides a microscopic basis for the time-superposition principle and predicts the macroscopic rheology of thermo-rheologically simple vitrimers.

Using Selectively Scaled Molecular Dynamics Simulations to Assess Ligand Poses in RNA Aptamers.

Predicting the structure (or pose) of RNA-ligand complexes is an important problem in RNA structural biology. Although one could use computational docking to rapidly sample putative poses of RNA-ligand complexes, accurately discriminating the native-like poses from non-native, decoy poses remains a formidable challenge. Here, we started from the assumption that native-like RNA-ligand poses are less likely to dissociate during molecular dynamics simulations, and then we used enhanced simulations to promote ligand unbinding for diverse poses of a handful of RNA aptamer-ligand complexes. By fitting unbinding profiles obtained from the simulations to a single exponential, we identified the characteristic decay time (τ) as particularly effective at resolving native poses from decoys. We also found that a simple regression model trained to predict the simulation-derived parameters directly from structure could also discriminate ligand poses for similar RNA aptamers. Characterizing the unbinding properties of individual poses may thus be an effective strategy for enhancing pose prediction for ligands interacting with RNA aptamers. A similar strategy might be applicable to other ligandable RNAs; however, further analysis will be required to confirm this hypothesis.