Temporal Decay Research Articles

The influence of initial perturbation power spectra on the growth of a turbulent mixing layer induced by Richtmyer–Meshkov instability

This paper investigates the influence of different broadband perturbations on the evolution of a Richtmyer–Meshkov turbulent mixing layer initiated by a Mach 1.84 shock traversing a perturbed interface separating gases with a density ratio of 3:1. Both the bandwidth of modes in the interface perturbation, as well as their relative amplitudes, are varied in a series of carefully designed numerical simulations at grid resolutions up to 3.2×109 cells. Three different perturbations are considered, characterised by a power spectrum of the form P(k)∝km where m=−1, −2 and −3. The growth of the mixing layer is shown to strongly depend on the initial conditions, with the growth rate exponent θ found to be 0.5, 0.63 and 0.75 for each value of m at the highest grid resolution. The asymptotic values of the molecular mixing fraction Θ are also shown to vary significantly with m; at the latest time considered Θ is 0.56, 0.39 and 0.20 respectively. Turbulent kinetic energy (TKE) is also analysed in both the temporal and spectral domains. The temporal decay rate of TKE is found not to match the predicted value of n=2−3θ, which is shown to be due to a time-varying normalised dissipation rate Cϵ. In spectral space, the data follow the theoretical scaling of k(m+2)∕2 at low wavenumbers and tend towards k−3∕2 and k−5∕3 scalings at high wavenumbers for the spectra of transverse and normal velocity components respectively. The results represent a significant extension of previous work on the Richtmyer–Meshkov instability evolving from broadband initial perturbations and provide useful benchmarks for future research.

Time and sequence awareness in similarity metrics for recommendation

Modeling the temporal context efficiently and effectively is essential to provide useful recommendations to users. In this work, we focus on improving neighborhood-based approaches where we integrate three different mechanisms to exploit temporal information. We first present an improved version of a similarity metric between users using a temporal decay function, then, we propose an adaptation of the Longest Common Subsequence algorithm to be used as a time-aware similarity metric, and we also redefine the neighborhood-based recommenders to be interpreted as ranking fusion techniques where the neighbor interaction sequence can be exploited by considering the last common interaction between the neighbor and the user.We demonstrate the effectiveness of these approaches by comparing them with other state-of-the-art recommender systems such as Matrix Factorization, Neural Networks, and Markov Chains under two realistic time-aware evaluation methodologies (per user and community-based). We use several evaluation metrics to measure both the quality of the recommendations – in terms of ranking relevance – and their temporal novelty or freshness. According to the obtained results, our proposals are highly competitive and obtain better results than the rest of the analyzed algorithms, producing improvements under the two evaluation dimensions tested consistently through three real-world datasets.

Diversity of temporal influence in popularity prediction of scientific publications

Predicting the future influential papers is a challenging issue witch has attracted many attentions. In this paper, we focused on the temporal information of citations to study the popularity prediction problem from the perspective of citation dynamics. The experimental study of the APS citation data shows that the temporal decay rate of the influence of citations is decay with paper’s age, and the decay rate is a power-law distribution. We introduced the diversity of temporal decay rate of the influence of citations to predict the future popularity of papers, and proposed a diverse temporal decay method. The result shows that this method can improve the prediction accuracy compared with other popularity-based prediction methods. More importantly, this method can detect some of the newly published papers that haven’t accumulated many citations but will quickly become popular in the future.

A comparison of characteristic parameters of mining related and tectonic seismic aftershock sequences

The temporal decay pattern of seismicity following rock bursts and large magnitude events is studied for aftershock sequences in several mines in Ontario, Canada. The decay phenomenon is described by the so – called Modified Omori’s law. The dependency of the parameters K, c and p with the magnitude of large mine seismic events is analyzed. A total of eleven mining related seismic sequences, with mainshock magnitudes ranging from 0.5 to 4.0 Mn (Nuttli magnitude scale) and from four different mine environments are examined. Results, including the calculation of the Gutenberg - Richter’s and Reasenberg – Jones parameters b and a’, are compared with previous research in tectonic seismicity using available data from New Zealand, Italy and U.S.A. Further parameters were derived and applied in a correlation study of mining related and tectonic events. The study revealed a good correlation between the productivity parameter a’ and b – values. Particularly, the b – values show significant different number ranges for mining related and tectonic data, which was applied to derive a direct numerical relationship between mining related and tectonic parameters and the aftershock number estimation. Finally, numerical values for the b – values in mining related seismic activity were obtained.

Emergent Behaviors of Lohe Tensor Flocks

We present a first-order aggregation model on a group ring, and study its asymptotic dynamics. In a positive coupling strength regime, we show that the flow generated by the proposed model tends to an equilibrium manifold asymptotically. For this, we introduce a Lyapunov functional which is non-increasing along the flow, and using the temporal decay of the nonlinear functional and the LaSalle invariance principle, we show that the flow converges toward an equilibrium manifold asymptotically. We also show that the structure of an equilibrium manifold is strongly dependent on the structure of an underlying group.

On the well-posedness and temporal decay for the 3D generalized incompressible Hall-MHD system

In this paper, we prove a new result on the properties of decay character $$r^*$$ (see Lemma 2.6) and then show a small data global well-posedness result for three-dimensional generalized incompressible Hall-MHD system. In the end, through Fourier splitting method, the properties of decay character $$r^*$$ and mathematical induction, we study the decay rate of higher-order spatial and time derivatives of strong solutions to such system.

Global existence and decay of solutions for hard potentials to the fokker-planck-boltzmann equation without cut-off

In this article we study the large-time behavior of perturbative classical solutions to the Fokker-Planck-Boltzmann equation for non-cutoff hard potentials. When the initial data is a small pertubation of an equilibrium state, global existence and temporal decay estimates of classical solutions are established.

Temporal decay of strong solutions to the magnetohydrodynamics with power-law type nonlinear viscous fluid

We show that the energy norm of strong solutions to the power-law type magnetohydrodynamics in three dimensions has a decay rate of t−34.

GRB 180620A: Evidence for Late-time Energy Injection

Abstract The early optical emission of gamma-ray bursts (GRBs) gives an opportunity to understand the central engine and first stages of these events. About 30% of GRBs present flares whose origin is still a subject of discussion. We present optical photometry of GRB 180620A with the COATLI telescope and RATIR instrument. COATLI started to observe from the end of prompt emission at T + 39.3 s and RATIR from T + 121.4 s. We supplement the optical data with the X-ray light curve from Swift/XRT. We observe an optical flare from T + 110 s to T + 550 s, with a temporal index decay α O,decay = 1.32 ± 0.01, and Δt/t = 1.63, which we interpret as the signature of a reverse shock component. After the initial normal decay the light curves show a long plateau from T + 500 s to T + 7800 s in both X-rays and the optical before decaying again after an achromatic jet break at T + 7800 s. Fluctuations are seen during the plateau phase in the optical. Adding to the complexity of GRB afterglows, the plateau phase (typically associated with the coasting phase of the jet) is seen in this object after the “normal” decay phase (associated with the deceleration phase of the jet), and the jet break phase occurs directly after the plateau. We suggest that this sequence of events can be explained by a rapid deceleration of the jet with t d ≲ 40 s due to the high density of the environment (≈100 cm−3) followed by reactivation of the central engine, which causes the flare and powers the plateau phase.

Turbulence and entrainment in an atmospheric pressure dielectric barrier plasma jet

AbstractParticle image velocimetry, laser‐induced fluorescence, and computational modeling are used to quantify the impact of plasma generation on air entrainment into a helium plasma jet. It is demonstrated that discharge generation yields a minor increase in the exit velocity of the gas. In contrast, the laminar to turbulent transition point is strongly affected, attributed to an increase in plasma‐induced perturbations within the jet shear layer. The temporal decay of laser‐induced fluorescence from OH is used as an indicator of humid air within the plasma. The results show that plasma‐induced perturbations increase the quenching rate of the OH‐fluorescent state; indicating that shear‐layer instabilities play a major role in determining the physicochemical characteristics of the plasma.

Generic parameters of first-order kinetics accurately describe soil organic matter decay in bare fallow soils over a wide edaphic and climatic range

The conventional soil organic matter (SOM) decay paradigm considers the intrinsic quality of SOM as the dominant decay limitation with the result that it is modelled using simple first-order decay kinetics. This view and modelling approach is often criticized for being too simplistic and unreliable for predictive purposes. It is still under debate if first-order models can correctly capture the variability in temporal SOM decay observed between different agroecosystems and climates. To address this question, we calibrated a first-order model (Q) on six long-term bare fallow field experiments across Europe. Following conventional SOM decay theory, we assumed that parameters directly describing SOC decay (rate of SOM quality change and decomposer metabolism) are thermodynamically constrained and therefore valid for all sites. Initial litter input quality and edaphic interactions (both local by definition) and microbial efficiency (possibly affected by nutrient stoichiometry) were instead considered site-specific. Initial litter input quality explained most observed kinetics variability, and the model predicted a convergence toward a common kinetics over time. Site-specific variables played no detectable role. The decay of decades-old SOM seemed mostly influenced by OM chemistry and was well described by first order kinetics and a single set of general kinetics parameters.

The temporal correlation transfer in layered bio-models

The temporal correlation functions are simulated for a two-layer model of a highly inhomogeneous medium which can be considered as the scull-brain imitation, or phantom. The temporal decay of correlations are considered for two different mechanisms of particle movement, either the Brownian diffusion, or the random velocity square mechanism. The results obtained are turned to be highly dependent on the form of the kinetics of scatterers.

Effects of quorum quenching on temporal succession of activated sludge microbial community in a membrane bioreactor.

Quorum quenching (QQ) is an attractive strategy for mitigating biofouling in membrane bioreactors (MBRs). However, the effects of QQ on the activated sludge (AS) process have not been adequately evaluated. This study investigated the long-term effects of QQ on a laboratory-scale anoxic-oxic MBR, focusing on AS performance and microbial community. Anoxic-oxic MBRs with and without QQ were operated for 91days. QQ did not affect COD and TN removal efficiencies over the experimental period, during which its activity remained >90%. QQ reduced floc size by approximately 8% but had no effect on biomass concentration. AS microbial communities were regularly analysed using massively parallel sequencing. AS bacterial communities were temporally dynamic irrespective of QQ presence, for example, a temporal increase in bacterial diversity and a temporal decay of community similarity. QQ counteracted the temporal change in diversity and the temporal distance-community decay. Community comparison revealed that QQ changed the successional trajectory of the AS community at a late period, because it decelerated temporal changes of specific members, such as Thiothrix and Sphingomonadaceae*. Correlation networks revealed that QQ increased network clustering, complexity and density. The combined results suggest that the tighter microbial association by QQ increased the community resistance. QQ can enhance the diversity and stability of the AS community in MBR by counteracting the innate temporal change in community structure. Our findings are useful for the further advancement of QQ-based strategies in engineered microbial environments.

Recent advances with electro-optic polymers

In recent years the electro-optic polymers emerged as an important branch of material science. This growth and interest is fundamentally motivated by practical application of these materials in second-order nonlinear optics and in waveguiding configuration. Indeed, these materials marry excellent optical quality of amorphous σ bonded polymers with enhanced first hyperpolarizability of imbedded organic nonlinear optical molecules. Although a big progress was achieved with them, concerning particularly the science, understanding and applications, some problems remain still incompletely solved, particularly the stability of induced polar order by the application of external electric field and the molecule aggregation. In this review paper we recall techniques of thin film fabrication, poling, characterization of NLO properties and discuss more precisely problems of molecule aggregation as well as the temporal decay of polar order. A novel 3D second-order NLO chromophores, namely the [2] paracyclophanes, which may help to limit the aggregation, are proposed. We show, in particular, that this molecule can be poled in doped PMMA thin films. Practical applications of electro-optic polymers are also reviewed and discussed.

Asymptotics of Chemotaxis Systems with Fractional Dissipation for Small Data in Critical Sobolev Space

A chemotaxis system with Newtonian attraction and fractional dissipation of order $\alpha \in (0,2)$ is considered in ${ \mathbb{R} }^{N}$ . For initial data belonging to $L^{1}\cap H^{4}$ but small in $L^{\frac{N}{ \alpha }}$ , $N=2,3$ , the temporal decay and the asymptotic behavior of a global classical solution are established. In particular, we derive a precise decay estimate for higher Sobolev norms.

An investigation of a novel reusable radiochromic sheet for 2D dose measurement.

Radiochromic film remains a useful and versatile clinical dosimetry tool. Current film options are single use. Here, we introduce a novel prototype two-dimensional (2D) radiochromic sheet, which optically clears naturally at room temperature after irradiation and can be reused. We evaluate the sheets for potential as a 2D dosimeter and as a radiochromic bolus with capability for dose measurement. A novel derivative of reusable Presage® was manufactured into thin sheets of 5mm thickness. The sheets contained 2% cumin-leucomalachitegreen-diethylamine (LMG-DEA) and plasticizer (up to 25% by weight). Irradiation experiments were performed to characterize the response to megavoltage radiation, including dose sensitivity, temporal decay rate, consistency of repeat irradiations, intra and inter-sheet reproducibility, multi-modality response (electrons and photons), and temperature sensitivity (22°C to 36°C). The local change in optical-density (ΔOD), before and after radiation, was obtained with a flat-bed film scanner and extracting the red channel. Repeat scanning enabled investigation of the temporal decay of ΔOD. Additional studies investigated clinical utility of the sheets through application to IMRT treatment plans (prostate and a TG119 commissioning plan), and a chest wall electron boost treatment. In the latter test, the sheet performed as a radiochromic bolus. The radiation induced OD change in the sheets was found to be proportional to dose and to exponentially decay to baseline in ~24h (R2=0.9986). The sheet could be reused and had similar sensitivity (within 1% after the first irradiation) for at least eight irradiations. Importantly, no memory of previous irradiations was observed within measurement uncertainty. The consistency of dose response from photons (6 and 15MV) and electrons (6-20MeV) was found to be within calibration uncertainty (~1%). The dose sensitivity of the sheets had a temperature dependence of 0.0012 ΔOD/°C. For the short (1min) single field IMRT QA verification, good agreement was observed between the Presage sheet and EBT film (gamma pass rate 97% at 3% 3mm dose-difference and distance-to-agreement tolerance, with a 10% threshold). For the longer (~13min) TG-119 9-field IMRT verification the gamma agreement was lower at 93% pass rate at 5% 3mm, 10% threshold, when compared with Eclipse. The lower rate is attributed to uncertainty arising from signal decay during irradiation and indicates a current limitation. For the electron cutout treatment, both Presage and EBT agreed well (within 2% RMS difference) but differed from the Eclipse treatment plan (~7% RMS difference) indicating some limitations to the Eclipse modeling in this case. The worst case estimates of uncertainty introduced by the signal decay for deliveries of 2, 5, and 10min are 0.6%, 1.4%, and 2.8% respectively. Reusable Presage sheets show promise for 2D dose measurement and as a radiochromic bolus for in vivo dose measurement. The current prototype is suitable for deliveries of length up to 5min, where the uncertainty introduced by signal decay is anticipated to be ~1% (worst case 1.4%), or for longer deliveries where there is no temporal modulation (e.g. physical compensators, or open beams). Additionally, spatial resolution is limited by sheet thickness and scanner resolution, resulting in a practical resolution of 0.8mm.

Narrow Spatial Aftershock Zones for Induced Earthquake Sequences in Oklahoma

AbstractThe current paradigm for estimating regional long‐term seismic hazard involves declustering whereby aftershocks are removed from an earthquake catalog to identify the underlying background seismicity rate. Inaccurate declustering can ultimately underestimate or overestimate the regional seismic hazard. In Oklahoma, estimating a background seismicity rate is complicated by the highly variable seismicity rate over the last decade. To improve conventional declustering methods used in hazard modeling in Oklahoma, we scrutinize the aftershock windows used for declustering and investigate how aftershocks decay in space and time to establish data‐driven parameters for aftershock windowing. We observe that the spatial decay of aftershocks is more rapid in Oklahoma than in Southern California, motivating the need for smaller spatial declustering windows in Oklahoma. Temporal aftershock decay is statistically indistinguishable between Oklahoma and Southern California, suggesting that temporal declustering windows derived for Southern California are likely sufficient for Oklahoma.

Retinal supplementation augments optogenetic stimulation efficacy in vivo

Objective. Over the last two decades, optical control of neuronal activity in the central nervous system has seen rapid development, demonstrating the utility of optogenetics as both an experimental and therapeutic tool. Conversely, applications of optogenetics in the peripheral nervous system have been relatively constrained by the challenges of temporally variable opsin expression, light penetration and immune attack of non-native opsins. Whilst opsin expression can be increased significantly through high-concentration viral induction, subsequent attack by the immune system causes temporal decay and high variability in electrophysiological response. Approach. In this study, we present a method to circumvent the aforementioned challenges by locally supplementing all-trans-retinal (ATR) (via a slow release pellet) to increase tissue photosensitivity in transgenic mice expressing channelrhodopsin 2 (ChR2) in nerves. Main results. In mice supplemented with ATR, we demonstrate enhanced electrophysiological activation and fatigue tolerance in response to optical stimulation for six weeks. Significance. Local supplementation of ATR enables improved optogenetic stimulation efficacy in peripheral nerves. This method enables greater exploration of neurophysiology and development of clinically-viable optogenetic treatments in the peripheral nervous system.

A Bandit-Based Ensemble Framework for Exploration/Exploitation of Diverse Recommendation Components

This work presents an extension of Thompson Sampling bandit policy for orchestrating the collection of base recommendation algorithms for e-commerce. We focus on the problem of item-to-item recommendations, for which multiple behavioral and attribute-based predictors are provided to an ensemble learner. In addition, we detail the construction of a personalized predictor based on k -Nearest Neighbors ( k NN), with temporal decay capabilities and event weighting. We show how to adapt Thompson Sampling to realistic situations when neither action availability nor reward stationarity is guaranteed. Furthermore, we investigate the effects of priming the sampler with pre-set parameters of reward probability distributions by utilizing the product catalog and/or event history, when such information is available. We report our experimental results based on the analysis of three real-world e-commerce datasets.

Preliminary investigation of a reusable radiochromic sheet for radiation dosimetry

This work investigates a novel reusable radiochromic sheet developed as an economic film substitute or as a radiochromic bolus. The radiation-induced optical density (OD) change of the sheet is read-out with a commercial flat-bed optical scanner. An optimized readout procedure was developed including an optimal scan-time window. Fundamental radiochromic properties of the sheets were characterized including temporal decay of OD, dose sensitivity and consistency through repeated irradiations, and temperature sensitivity. The radiation induced OD change in the sheets was found to decay to baseline within ~24 hours, after which the sheet could be reused. The sensitivity of subsequent re-irradiations was found to be consistent within ±5% (coefficient of variation of 4.5%) for at least 6 irradiations and potentially many more. Importantly, the sheets were not observed to carry any detectable memory of previous irradiations within measurement uncertainty. In conclusion, the Presage sheets show promise as an economic multi-purpose alternative for film applications and potentially as a radiochromic bolus. Further work is required to test the sheet in diverse clinical applications, and to develop a softer material for bolus applications.