Temporal Decay Research Articles

The determination of highly time-resolved and source-separated black carbon emission rates using radon as a tracer of atmospheric dynamics

Abstract. We present a new method for the determination of the source-specific black carbon emission rates. The methodology was applied in two different environments: an urban location in Ljubljana and a rural one in the Vipava valley (Slovenia, Europe), which differ in pollution sources and topography. The atmospheric dynamics was quantified using the atmospheric radon (222Rn) concentration to determine the mixing layer height for periods of thermally driven planetary boundary layer evolution. The black carbon emission rate was determined using an improved box model taking into account boundary layer depth and a horizontal advection term, describing the temporal and spatial exponential decay of black carbon concentration. The rural Vipava valley is impacted by a significantly higher contribution to black carbon concentration from biomass burning during winter (60 %) in comparison to Ljubljana (27 %). Daily averaged black carbon emission rates in Ljubljana were 210 ± 110 and 260 ± 110 µgm-2h-1 in spring and winter, respectively. Overall black carbon emission rates in Vipava valley were only slightly lower compared to Ljubljana: 150 ± 60 and 250 ± 160 µgm-2h-1 in spring and winter, respectively. Different daily dynamics of biomass burning and traffic emissions was responsible for slightly higher contribution of biomass burning to measured black carbon concentration, compared to the fraction of its emission rate. Coupling the high-time-resolution measurements of black carbon concentration with atmospheric radon concentration measurements can provide a useful tool for direct, highly time-resolved measurements of the intensity of emission sources. Source-specific emission rates can be used to assess the efficiency of pollution mitigation measures over longer time periods, thereby avoiding the influence of variable meteorology.

Localized Afterslip at Geometrical Complexities Revealed by InSAR After the 2016 Central Italy Seismic Sequence

AbstractThe Mw 6.5 Norcia earthquake occurred on 30 October 2016, along the Mt Vettore fault (Central Apennines, Italy), it was the largest earthquake of the 2016–2017 seismic sequence that started 2 months earlier with the Mw 6.0 Amatrice earthquake (24 August). To detect potential slow slip during the sequence, we produced Interferometric Synthetic Aperture Radar (InSAR) time series using 12‐ to 6‐day repeat cycles of Sentinel‐1A/1B images. Time series indicates that centimeter‐scale surface displacements took place during the 10 weeks following the Norcia earthquake. Two areas of subsidence are detected: one in the Castelluccio basin (hanging wall of the Mt Vettore fault) and one in the southern extent of the Norcia earthquake surface rupture, near an inherited thrust. Poroelastic and viscoelastic models are unable to explain these displacements. In the Castelluccio basin, the displacement reaches 13.2 ± 1.4 mm in the ascending line of sight on 6 January 2017. South of the Norcia earthquake surface rupture (a zone between the Norcia and Amatrice earthquakes), the postseismic surface displacements affect a smaller area but reach 35.5 ± 1.7 mm in ascending line of sight by January 2017 and follow a logarithmic temporal decay consistent with postseismic afterslip. Our analysis suggests that the structurally complex area located south of the Norcia rupture (30 October) is characterized by a conditionally stable frictional regime. This geometrical and frictional barrier likely halted rupture propagation during the Amatrice (24 August) and Norcia (30 October) earthquakes at shallow depth (<3–4 km).

The impact of ultraviolet laser excitation during Raman spectroscopy of hexagonal boron nitride thin films

AbstractWe utilized excitation in the ultraviolet (UV) spectral range for the study of hexagonal boron nitride (h‐BN) thin films on different substrates by Raman spectroscopy. Whereas UV excitation offers fundamental advantages for the investigation of h‐BN and heterostructures with graphene, the actual Raman spectra recorded under ambient conditions reveal a temporal decay of the signal intensity. The disappearance of the Raman signal is found to be induced by thermally activated chemical reactions with ambient molecules at the h‐BN surface. The chemical reactions could be strongly suppressed under vacuum conditions which, however, favor the formation of a carbonaceous surface contamination layer. For the improvement of the signal‐to‐noise ratio under ambient conditions, we propose a line‐scan method for the acquisition of UV Raman spectra in atomically thin h‐BN, a material which is expected to play a key role in future technologies based on 2D van der Waals heterostructures.

Elastic Character of Seismic Coda Envelopes Within East Indian Shield

Seismic codas are usually characterized by the values of coda Q (Qc). However, interpretation of this quantity is often tricky because of its frequency dependence and acute sensitivity to subjective theoretical assumptions and processing parameters. Here, a simpler and physically more consistent parameterization of coda envelopes is proposed by noting that their temporal decay rates are often nearly frequency-independent. This weak frequency dependence shows that codas mostly consist of elastic reverberations and scattering on larger-scale structures, and the subwavelength-scale scattering and Q-type wave attenuation are weak. A recent study of the eastern Indian Shield by Singh et al. (in this journal) gives an illustration of such elastic coda. From that study, the inferred Qc steeply increases with frequency, lapse times, window lengths, and distances from the seismic station. However, we show that all of these dependencies of Qc represent a common artifact of the acquisition geometry and inversion procedure. In an alternate interpretation, we explain the same coda envelopes by two frequency-independent properties of the Earth’s subsurface: geometrical attenuation denoted γc,Earth and effective Q denoted Qc,Earth. Based on these parameters, the model becomes independent of theoretical assumptions and comparable to other areas, and the acquisition/inversion artifact is reduced. The estimated γc,Earth is above 0.01 s−1, which is also found in other areas of active tectonics. The effective attenuation is weak (Qc,Earth > 5700, likely below the measurable level), which is typical for stable tectonic areas. The data indicate near-surface resonances beneath the recording station. Effects of these resonances on coda envelopes also exceed those of Q-type attenuation. Thus, in the eastern Indian Shield and likely many other areas, coda envelopes are principally controlled by elastic structures such as crustal and near-surface layering, and not necessarily by the S-wave Q and uniformly-distributed random, small-scale scattering as commonly thought.

On Global Well-Posedness and Temporal Decay for 3D Magnetic Induction Equations with Hall Effect

The main purpose of this paper is to study the global existence and uniqueness of solutions for three-dimensional incompressible magnetic induction equations with Hall effect provided that ∥u0∥H32+ε+∥b0∥H2(0<ε<1) is sufficiently small. Moreover, using the Fourier splitting method and the properties of decay character r*, one also shows the algebraic decay rate of a higher order derivative of solutions to magnetic induction equations with the Hall effect.

Stability and temporal decay of nanopatterned tribocharge on nanotextured elastomer surfaces

Contact electrification of nanotextured elastomer surfaces often generates nanopatterned tribocharges that are useful for both scientific and practical purposes. For sustained utilization of the nanopatterned tribocharge, their stability and temporal behavior must be characterized and studied. It is, however, a highly challenging task as it requires long-term, repeated probing of the tribocharge at the nanoscale spatial resolution. In this work, we performed such a comprehensive experimental study of nanopatterned tribocharges on elastomer surfaces using Kelvin probe force microscopy (KPFM) and electrostatic force microscopy (EFM). Curve-fitting analysis of the KPFM results not only affirmed the temporally decaying nature of the tribocharge but also separated them into two distinct, fast and slowly decaying, components that could be attributed to two different tribocharging mechanisms. Through pre-constrained optimization of the curve-fitting parameters and comparison of the results, we could attribute the fast and slow decay components to the tribocharges generated by tangential sliding and surface-normal separation of the material interface, respectively. The analysis also enabled us to estimate time-invariant “pedestal” potentials from the KPFM results and predict the existence of long-term stable tribocharge on the nanotextured elastomer surface. We experimentally confirmed it by re-scanning the specimens 14 days after the initial measurements. The observations, analysis, and the mechano-triboelectric charging model will benefit not only the researchers of nanoscale tribocharges but also those interested in the study and applications of triboelectricity in general. • Observed how nanopatterned tribocharge decays in time using long-term KPFM. • Identified fast and slow decays and correlated them with surface nano-morphology. • Attributed the two tribocharges to different triboelectrification mechanisms. • Predicted long-term stable tribocharge and confirmed it via KPFM at the 14th day.

Fundamental Limit of Phase Coherence in Two-Component Bose-Einstein Condensates.

We experimentally and theoretically study phase coherence in two-component Bose-Einstein condensates of ^{87}Rb atoms on an atom chip. Using Ramsey interferometry we determine the temporal decay of coherence between the |F=1,m_{F}=-1⟩ and |F=2,m_{F}=+1⟩ hyperfine ground states. We observe that the coherence is limited by random collisional phase shifts due to the stochastic nature of atom loss. The mechanism is confirmed quantitatively by a quantum trajectory method based on a master equation which takes into account collisional interactions, atom number fluctuations, and losses in the system. This decoherence process can be slowed down by reducing the density of the condensate. Our findings are relevant for experiments on quantum metrology and many-particle entanglement with Bose-Einstein condensates and the development of chip-based atomic clocks.

Exploiting complex medical data with interpretable deep learning for adverse drug event prediction.

A variety of deep learning architectures have been developed for the goal of predictive modelling and knowledge extraction from medical records. Several models have placed strong emphasis on temporal attention mechanisms and decay factors as a means to include highly temporally relevant information regarding the recency of medical event occurrence while facilitating medical code-level interpretability. In this study we utilise such models with a large Electronic Patient Record (EPR) data set consisting of diagnoses, medication, and clinical text data for the purpose of adverse drug event (ADE) prediction. The first contribution of this work is an empirical evaluation of two state-of-the-art medical-code based models in terms of objective performance metrics for ADE prediction on diagnosis and medication data. Secondly, as an extension of previous work, we augment an interpretable deep learning architecture to permit numerical risk and clinical text features and demonstrate how this approach yields improved predictive performance compared to the other baselines. Finally, we assess the importance of attention mechanisms in regards to their usefulness for medical code-level and text-level interpretability, which may facilitate novel insights pertaining to the nature of ADE occurrence within the health care domain.

Quasideterministic dynamics, memory effects, and lack of self-averaging in the relaxation of quenched ferromagnets.

We discuss the interplay between the degree of dynamical stochasticity, memory persistence, and violation of the self-averaging property in the aging kinetics of quenched ferromagnets. We show that, in general, the longest possible memory effects, which correspond to the slowest possible temporal decay of the correlation function, are accompanied by the largest possible violation of self-averaging and a quasideterministic descent into the ergodic components. This phenomenon is observed in different systems, such as the Ising model with long-range interactions, including the mean-field, and the short-range random-field Ising model.

Photoluminescence properties of hybrid perovskites in solar cells with TiO2 and Mg0.2Zn0.8O electron transport layers

This paper presents a study of the photoluminescence properties of hybrid perovskite films deposited on titanium and magnesium zinc oxide films, as electron transport layers, using the spin-coating technique. The subject of the investigation was continuous wave photoluminescence versus temperature, excitation power and transient photoluminescence. Moreover, the paper discusses possible carrier recombination mechanisms. Complex temporal decay was approximated through the use of several models, but only the four-exponent model and the model using the sum of two hyperbolic functions provided a good agreement with the experimental data. The first attempt to replace titanium dioxide with magnesium zinc oxide in conjunction with the perovskite layer showed improved optical properties such as a weaker non-radiative recombination process and a longer decay time constant.

Enhancement of Resolution and Propagation Length by Sources with Temporal Decay in Plasmonic Devices

Highly lossy nature of metals has severely limited the scope of practical applications of plasmonics. The conventional approach to circumvent this limitation has been to search for new materials with more favorable dielectric properties (e.g., reduced loss), or to incorporate gain media to overcome the inherent loss. In this study, however, we turn our attention to the source and show that the wealth of new SPP modes with simultaneous complex frequencies and complex wave vectors that are otherwise unreachable can be excited by imposing temporal decay on the excitation. Therefore, to understand the possible implications of these new modes and how to be able to tune them for specific applications, we propose a framework of pseudo-monochromatic modes that are generated by introducing exponential decays into otherwise monochromatic sources. Within this framework, the dispersion relation of complex SPPs is re-evaluated and cast to be a surface rather than a curve, depicting all possible ω − k pairs (both complex in general) that are supported by the given geometry. To demonstrate the potentials of the complex modes and the use of the framework to study them selectively, we have chosen two important, and somewhat limiting, features of SPPs to investigate; resolution in plasmonic lenses and propagation length in SPP waveguides. While the former is mainly used to validate the proposed method and the framework on the recent improvement of resolution in plasmonic superlenses, the latter provides a novel approach to extend the propagation length of the SPP modes in planar waveguides significantly. Since the improvement in propagation length due to the introduction of temporal decay to the excitation is rather counter-intuitive, the dispersion-based theoretical predictions (the proposed approach) have been validated via the FDTD simulations of Maxwell’s equations in the same geometry without any a priori assumptions on the frequency or the wave vector.

Candle flame soot sizing by planar time-resolved laser-induced incandescence

Soot emissions from flaming combustion are relevant as a significant source of atmospheric pollution and as a source of nanomaterials. Candles are interesting targets for soot characterization studies since they burn complex fuels with a large number of carbon atoms, and yield stable and repeatable flames. We characterized the soot particle size distributions in a candle flame using the planar two-color time-resolved laser induced incandescence (2D-2C TiRe-LII) technique, which has been successfully applied to different combustion applications, but never before on a candle flame. Soot particles are heated with a planar laser sheet to temperatures above the normal flame temperatures. The incandescent soot particles emit thermal radiation, which decays over time when the particles cool down to the flame temperature. By analyzing the temporal decay of the incandescence signal, soot particle size distributions within the flame are obtained. Our results are consistent with previous works, and show that the outer edges of the flame are characterized by larger particles (approx 60,hbox {nm}), whereas smaller particles (approx 25,hbox {nm}) are found in the central regions. We also show that our effective temperature estimates have a maximum error of 100 K at early times, which decreases as the particles cool.

Impact of variability in decay coefficients on simulating monochloramine dissipation in storm sewers

Concerns about total residual chlorine effects on the aquatic environment have led to a lowering of allowable effluent discharge concentrations. Many municipalities use monochloramine as a water disinfectant, which makes its way into drainage systems through outdoor and industrial water uses, and ultimately into surface waters. Monochloramine is known to dissipate with variable temporal and spatial decay coefficients; however, no existing stormwater models simulate these aspects. Thus, this study describes a novel Variable Decay Coefficient Simulator (VDCS) that predicts levels of degradable pollutants in sewer systems. The importance of spatially- and temporally-varying monochloramine decay coefficients on pollutant concentrations was assessed through three scenarios using, (1) a constant decay coefficient, (2) spatially-varying decay coefficients per land-use, and (3) spatially- and temporally-varying decay coefficients. At the system outfall, the spatially- and temporally-varying decay coefficients generated 67% and 100% higher concentrations, respectively, than the constant decay coefficient. These differences have important implications for the modeling of degradable pollutants in stormwater systems, and for the application of environmental regulations.

A Critical, Event-Related Appraisal of Denoising in Resting-State fMRI Studies.

This article advances two parallel lines of argument about resting-state functional magnetic resonance imaging (fMRI) signals, one empirical and one conceptual. The empirical line creates a four-part organization of the text: (1) head motion and respiration commonly cause distinct, major, unwanted influences (artifacts) in fMRI signals; (2) head motion and respiratory changes are, confoundingly, both related to psychological and clinical and biological variables of interest; (3) many fMRI denoising strategies fail to identify and remove one or the other kind of artifact; and (4) unremoved artifact, due to correlations of artifacts with variables of interest, renders studies susceptible to identifying variance of noninterest as variance of interest. Arising from these empirical observations is a conceptual argument: that an event-related approach to task-free scans, targeting common behaviors during scanning, enables fundamental distinctions among the kinds of signals present in the data, information which is vital to understanding the effects of denoising procedures. This event-related perspective permits statements like "Event X is associated with signals A, B, and C, each with particular spatial, temporal, and signal decay properties". Denoising approaches can then be tailored, via performance in known events, to permit or suppress certain kinds of signals based on their desirability.

Multiscale Modeling and Simulation of Heat Transfer between Alumina Nanoparticles and Helium Gas

Multiscale modeling and simulation of heat transfer between alumina nanoparticles and helium gas is conducted. Density functional theory (DFT) simulations are first performed to calculate adsorption energies and derive pair potentials for alumina-helium system. The obtained well depths are 2.794 meV and 0.921 meV for Al-He and O-He interactions, substantially lower than the values obtained using the Lorentz-Berthelot mixing rules. Subsequently, DFT derived potentials are used to conduct molecular dynamics (MD) simulations and calculate accommodation coefficients for solid temperatures in the range of 1700-2100 K and gas temperature of 300 K. The calculated accommodation coefficients are of the order of 0.1 and are weakly dependent on the solid temperature. Predictions are within the upper bound of 0.4 obtained using Altman's model for materials and conditions considered in the present study. MD derived accommodation coefficients are then fed as inputs to a macroscopic heat transfer model to predict temporal evolution of temperature of an alumina nanoparticle placed in helium gas. The proposed model captures the temporal decay of particle temperature reasonably well until about 200 ns. The disparity between predictions and experimental data is primarily attributed to different reasons such as heating up of the gas in a confined environment and sintering and aggregation of particles.

The rate of forgetting over time in working memory during early childhood

The detrimental effect of delays of retention on working memory has been a source of constant debate since the fifties. While studies in adults have proposed that temporal decay or interference underlie this effect, developmental change in the rate of forgetting is often mentioned to account for the developmental growth in working memory capacity. However, forgetting rate has never been examined in early childhood, and the few studies in older children led to divergent findings about the age-related change in the speed of forgetting. The present study documented for the first time this effect in early childhood. Using the shopping span task, children aged from 2;6 to 3;6 years observed the experimenter filling a bag with a series of plastic fruits and had to reproduce the series after various delays. Although their recall decreased with longer delays, the rate of forgetting on span was not affected by age, and the slope of linear regression between span and delay was similar across the three age groups. These findings suggest that forgetting rate did not evolve throughout early childhood, and as a consequence, the age-related increase in working memory capacity should be accounted for by changes in other processes than the rate of forgetting. Our results also pointed to important individual differences in early childhood that should be explored to broaden our understanding of working memory functioning in kindergarteners.

Lowly Polarized Light from a Highly Magnetized Jet of GRB 190114C

Abstract We report multicolor optical imaging and polarimetry observations of the afterglow of the first TeV-detected gamma-ray burst (GRB), GRB 190114C, using the RINGO3 and MASTER II polarimeters. Observations begin 31 s after the onset of the GRB and continue until ∼7000 s postburst. The light curves reveal a chromatic break at ∼400–500 s, with initial temporal decay α = 1.669 ± 0.013 flattening to α ∼ 1 postbreak, which we model as a combination of reverse and forward shock components with magnetization parameter R B ∼ 70. The observed polarization degree decreases from 7.7% ± 1.1% to 2%–4% 52–109 s postburst and remains steady at this level for the subsequent ∼2000 s at a constant position angle. Broadband spectral energy distribution modeling of the afterglow confirms that GRB 190114C is highly obscured (A v,HG = 1.49 ± 0.12 mag; cm−2). We interpret the measured afterglow polarization as intrinsically low and dominated by dust —in contrast to the P > 10% measured previously for other GRB reverse shocks—with a small contribution from polarized prompt photons in the first minute. We test whether first- and higher-order inverse Compton scattering in a magnetized reverse shock can explain the low optical polarization and subteraelectronvolt emission but conclude that neither is explained in the reverse shock inverse Compton model. Instead, the unexpectedly low intrinsic polarization degree in GRB 190114C can be explained if large-scale jet magnetic fields are distorted on timescales prior to reverse shock emission.

Temporal decay of a global solution to 3D magnetohydrodynamic system in critical spaces

Temporal decay of a global solution to 3D magnetohydrodynamic system in critical spaces

The effect of a step change in seabed depth on spreading discharged brine effluents from a two-outfall system

Discharged brine effluents from coastal desalination plants through marine outfall systems contain some reactive chemicals that may be derived from corrosion product, toxic antifoulants, antiscalants and other chemicals used in desalinating seawater. These effluents are subject to significant loss due to temporal decay that varies with water depth as the results of consumption by bacteria or radioactive decay, heat loss or evaporation through the surface, and break up or dissolution by turbulence. A far-field model using a two-dimensional decay-advection-diffusion equation with two point sources in a simple step seabed profile is presented to study the variability of decay with water depth. Analytical solutions are illustrated graphically by plotting contours of concentration to simulate the spreading of discharged brine effluent plumes from two outfalls in coastal waters. The maximum value of the compounded concentration at the shoreline is formulated and used as a measure for assessing the quality standards of coastal waters. It is found that, for coastal effluent discharges, the modern engineering practice which installs a two-port diffuser at the end of the outfall pipeline does produce low potential environmental impact.

Omori-like slow decay (p\u2009

We infer the postseismic deformation mechanisms following the 2011 Tohoku megathrust earthquake via an analysis of onshore geodetic observations. We focus on the temporal decay characteristics of postseismic deformation using continuous time-series data at time scales that span many orders of magnitude by means of high-rate GNSS data. Our analysis indicates Omori-like power-law decay of the horizontal ground displacement rates, with p-value (0.69) that is significantly smaller than that of the aftershock occurrence (~ 1). This slow decay implies a (non-Maxwellian) viscoelastic relaxation mechanism other than afterslip since immediately after the mainshock, which is inferred using only onshore geodetic data. Spatial distribution of the Omori parameters implies that the postseismic deformation will continue over 100 years in a down-dip area of the northern part of the mainshock fault. The decay characteristics of vertical displacement rates are also almost Omori-like, but data deviation from the fitting line several 100 days after the mainshock might reflect the change of the dominant mechanism of the postseismic deformation. This multi-time scale geodetic approach will provide important constraints for future viscoelastic models of Earth’s interior.