The population‐attributable fraction (PAF) is commonly interpreted as the proportion of events that can be ascribed to a certain exposure in a certain population. Its estimation is sensitive to ...common forms of time‐dependent bias in the face of a time‐dependent exposure. Predominant estimation approaches based on multistate modeling fail to fully eliminate such bias and, as a result, do not permit a causal interpretation, even in the absence of confounding. While recently proposed multistate modeling approaches can successfully eliminate residual time‐dependent bias, and moreover succeed to adjust for time‐dependent confounding by means of inverse probability of censoring weighting, inadequate application, and misinterpretation prevails in the medical literature. In this paper, we therefore revisit recent work on previously proposed PAF estimands and estimators in settings with time‐dependent exposures and competing events and extend this work in several ways. First, we critically revisit the interpretation and applied terminology of these estimands. Second, we further formalize the assumptions under which a causally interpretable PAF estimand can be identified and provide analogous weighting‐based representations of the identifying functionals of other proposed estimands. This representation aims to enhance the applied statistician's understanding of different sources of bias that may arise when the aim is to obtain a valid estimate of a causally interpretable PAF. To illustrate and compare these representations, we present a real‐life application to observational data from the Ghent University Hospital ICUs to estimate the fraction of ICU deaths attributable to hospital‐acquired infections.
Estimating the potential risk associated with an exposure occurring over time requires complex statistical techniques, since ignoring the time from study entry until the exposure leads to potentially ...seriously biased effect estimates. A prominent example is estimating the effect of hospital‐acquired infections on adverse outcomes in patients admitted to the intensive care unit. Exposure density sampling has been proposed as an approach to dynamic matching with respect to a time‐dependent exposure. Firstly, exposure density sampling can be useful to reduce the workload of study follow up, as it includes all exposed but only a subset of the not yet exposed individuals. Secondly, it can help to obtain a comparable control group by including propensity score matching. In the present article, we provide the theoretical justification that data obtained by exposure density sampling can be analyzed as a left‐truncated cohort. It is shown that exposure density sampling allows estimation of the effect of a time‐dependent exposure as well as further baseline covariates on a subsequent event, with only minor loss in precision as compared with a full cohort analysis. The sampling is applied to a real data example (hospital‐acquired infections in intensive care units) and in a simulation study. We also provide an estimate of the loss in precision in terms of an increased standard error in the reduced data set after exposure density sampling as compared with the full cohort.
The development of phosphorescent materials with time‐dependent phosphorescence colors (TDPCs) is of considerable interest for application in advanced dynamic information encryption. In this study, ...TDPC is realized in carbon dots (CDs) synthesized by the one‐pot hydrothermal treatment of levofloxacin. CD ink printed on paper (CD@paper) exhibits a change in phosphorescence color from orange to green, 1 s after irradiation with 395 nm light. However, when irradiated with wavelengths shorter or longer than 395 nm, the CD@paper exhibits only green or red phosphorescence, respectively. The red and green phosphorescence originates from the low‐energy surface oxide triplet state and high‐energy N‐related triplet state, respectively. When irradiated with a suitable light energy (around 395 nm wavelength), the two phosphorescent centers can be simultaneously activated, emitting red and green phosphorescence with different decay rates. The red and green phosphorescence merge into an orange phosphorescence initially, exhibiting the TDPC phenomenon. Based on the unusual phosphorescent properties of the CDs, a kind of multilevel, dynamic phosphorescence colored 3D code is designed for advanced dynamic information encryption.
Time‐dependent phosphorescence color (TDPC) change from orange to green is realized in carbon dots (CDs) for advanced dynamic information encryption. The TDPC arises from the dual phosphorescence centers of the CDs having different decay rates, which can be simultaneously activated by irradiating with a suitable light energy (around 395 nm).
In this article, we studied the system of a (2+1) dimensional Dirac equation in a time-dependent noncommutative phase-space. More specifically, we investigated the analytical solution of the ...corresponding system by the Lewis-Riesenfeld invariant method based on the construction of the Lewis-Riesenfeld invariant. Knowing that we obtained the time-dependent Dirac Hamiltonian of the problem in question from a time-dependent Bopp-Shift translation, then used it to set the Lewis- Riesenfeld invariant operators. Thereafter, the obtained results were used to express the eigenfunctions that lead to determining the general solution of the system.
Microscopic methods and tools to describe nuclear dynamics have considerably been improved in the past few years. They are based on the time-dependent Hartree–Fock (TDHF) theory and its extensions to ...include pairing correlations and quantum fluctuations. The TDHF theory is the lowest level of approximation of a range of methods to solve the quantum many-body problem, showing its universality to describe many-fermion dynamics at the mean-field level. The range of applications of TDHF to describe realistic systems allowing for detailed comparisons with experiment has considerably increased. For instance, TDHF is now commonly used to investigate fusion, multi-nucleon transfer and quasi-fission reactions. Thanks to the inclusion of pairing correlations, it has also recently led to breakthroughs in our description of the saddle to scission evolution, and, in particular, the non-adiabatic effects near scission. Beyond mean-field approaches such as the time-dependent random-phase approximation (TDRPA) and stochastic mean-field methods have reached the point where they can be used for realistic applications. We review recent progresses in both techniques and applications to heavy-ion collision and fission.
This study investigates time-dependent free convection heat transfer and buoyancy-assisted flow over a horizontal heated plate within a vertical channel for two distinct scenarios: one stand alone ...and second involving tilted plates and varying plate positions. The temperature difference between the plate and air induces buoyant airflow. The study explores the impact of plate tilt angles and positions on time-dependent heat transfer coefficients due to varying buoyant airflow. The primary focus of the research for both classes of study is on the effects of the tilt angles (which control the change in flow blockage ratio) and positions of the heated plate on the time-dependent heat transfer coefficients due to the time-dependent buoyant airflow. As the blockage ratio increases and the positions of the heated plate in the vertical channel decreases, the influence of time-dependent buoyancy on the time-dependent Nusselt number weakens. The time-dependent Richardson's number varied from 7.4 to 9.6 throughout the tests. Based on the experimental data gathered from corresponding flux geometries and test conditions, the CFD model was validated. We have also developed a set of empirical correlations for predicting time-dependent Nusselt numbers for a time-dependent Rayleigh number range of 2000 < Ra < 7500, the dimensionless height of the heated plate from 0.507 ≤
ϕ
≤ 0.551, and a flow blockage ratio of 0.08 ≤
χ
≤ 0.024. At orientations where
γ
= π/2
and
γ
= π/4
, it has been observed that the heat transfer at position
∅
1
is higher, whereas at
γ
= 0 orientation,
∅
1
heat transfer value is lower compared to the others. When the time required for the heated plate at all positions
(
∅
)
to reach thermal equilibrium with the ambient environment is compared with respect to orientation angles, it has been observed that the
γ
= π/2
orientation angle reaches thermal equilibrium in the shortest time compared to the
γ
= π/0
and
γ
= π/4
orientation angles.
This paper is concerned with H∞ filtering for a class of switched linear systems in discrete-time domain. A more general class of switching signals, the persistent dwell-time (PDT) switching is ...considered rather than the dwell-time or average dwell-time switching often studied in the literature. The concept on a stage of switching in the type of PDT switching signals is introduced, and each stage consists of a period of persistence and a dwell-time portion in which no switching occurs. A proper Lyapunov function suitable to the PDT switching is constructed, which is not only mode-dependent but also quasi-time-dependent (QTD). Then, a QTD filter is designed such that the resulting filtering error system is globally uniformly asymptotically stable and has a guaranteed H∞ noise attenuation performance. Certain techniques are explored such that the obtained performance index is of strictly non-weighted H∞ norm, which contrasts with the weighted (or called exponential) ones, i.e., weaker noise attenuation in the existing literature of switched systems with average dwell-time. An example of mass–spring system is provided to show the validity and potential of the developed results.
Achieving persistent room‐temperature phosphorescence (p‐RTP), particularly those of tunable full‐colors, from pure organic amorphous polymers is attractive but challenging. Particularly, those with ...tunable multicolor p‐RTP in response to excitation wavelength and time are highly important but both fundamentally and technically underexplored. Here, a facile and general strategy toward color‐tunable p‐RTP from blue to orange‐red based on amidation grafting of luminophores onto sodium alginate (SA) chains, resulting in amorphous polymers with distinct p‐RTP and even impressively excitation‐dependent and time‐dependent afterglows is reported. p‐RTP is associated with the unique semi‐rigidified SA chains, effective hydrogen bonding network, and oxygen barrier properties of SA, whereas excitation‐dependent and time‐dependent afterglows should stem from the formation of diversified p‐RTP emissive species with comparable but different lifetimes. These results outline a rational strategy toward amorphous smart luminophores with colorful, excitation‐dependent, and time‐dependent p‐RTP, excellent solution processability, and film‐forming ability for versatile applications.
Smart afterglow rainbow: A facile and efficient strategy is developed to achieve colorful persistent room‐temperature phosphorescence from blue to orange‐red in purely organic amorphous polymers with outstanding film‐forming ability. Moreover, excitation‐dependent and time‐dependent afterglows under ambient conditions are accessed owing to the formation of diversified clustered chromophores. Such exceptional emission behaviors and excellent processability render them promising for advanced technical applications.
Aiming at accurately and efficiently solve the Time-dependent Reliability Based Design Optimization (T-RBDO), two advanced solution strategies respectively called Time-dependent Sequential ...Optimization and Reliability Assessment (T-SORA) and Time-dependent Single Loop Approach (T-SLA) are established. Before constructing the T-SORA and T-SLA, a two-stage optimization is firstly established, in which the first stage makes the minimum instantaneous reliability indexes of probabilistic constraints satisfy reliability index targets and the second stage performs the time-dependent reliability indexes to match the reliability index targets. Two equivalent time-independent RBDOs are obtained based on the established two-stage optimization, and the key point is estimating the Minimum Performance Target Point (MPTP) in each stage. Two single optimization processes are constructed in T-SORA to efficiently estimate MPTPs in its two stages respectively. Two sequential single procedures are established in T-SLA to efficiently solve MPTPs and design parameter solutions in its two stages respectively, in which a new MPTP searching technique named Angle Descent Mean Value (ADMV) is proposed to approximate MPTP in each iteration. Furthermore, time-dependent reliability analysis is only required in the second stage, which will further improve the computational efficiency. Several numerical and engineering examples are introduced to show the effectiveness of the proposed T-SORA and T-SLA for solving T-RBDO.
•Two advanced solution strategies are proposed for T-RBDO.•Two-stage optimization is established to construct equivalent time-independent RBDO.•New MPTP searching technique is proposed in the optimization.•Time-dependent reliability analysis is only needed in the established second stage.
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