Decay Time Distribution Research Articles

Modal identification as a tool to increase the accuracy of acoustic absorption measurements in reverberation rooms

Measuring the acoustic properties of materials may be very challenging. At low frequencies, the sample may interfere with the room's modal behavior. When it occurs, the longest modal decays are influenced. Differences in reverberation time - empty Vs with-specimen conditions - are often emphasized by these modal effects, and, as a matter of fact, the absorption coefficient may be overestimated. The present work aims to increase the accuracy through data augmentation at low frequencies. Modal identification was performed on measured impulse responses of porous specimens, allowing the determination of modal-decay times within the third-octave bands of 80-160 Hz. A statistical analysis of natural modes highlights the modes whose decay exceeds the density function as outliers. This preliminary study ultimately provides some statistical considerations on the modal distribution of decay times and their relationship with the reverberation time measured through the Schroeder integral.

Limitations of the rate-distribution formalism in describing luminescence quenching in the presence of diffusion.

When encountering complex fluorescence decays that deviate from exponentiality, a very appealing approach is to use lifetime or rate constant distributions. These are related by Laplace transform to the sum of exponential functions, stretched exponentials, Becquerel's decay function, and others. However, the limitations of this approach have not been sufficiently discussed in the literature. In particular, the time-independent probability distributions of the rate constants or decay times are occasionally used to describe bimolecular quenching. We show that in such a case, this mathematical formalism has a clear physical interpretation only when the fluorophore and quencher molecules are immobile, as in the solid state. However, such an interpretation is no longer possible once we consider the motion of fluorophores with respect to quenchers. Therefore, for systems in which the relative motion of fluorophores and quenchers cannot be neglected, it is not appropriate to use the time-independent rate or decay time distributions to describe, fit, or rationalize experimental results on fluorescence decay.

Highly Indistinguishable Single Photons from Droplet-Etched GaAs Quantum Dots Integrated in Single-Mode Waveguides and Beamsplitters.

Integration of on-demand quantum emitters into photonic integrated circuits (PICs) has drawn much attention in recent years, as it promises a scalable implementation of quantum information schemes. A central property for several applications is the indistinguishability of the emitted photons. In this regard, GaAs quantum dots (QDs) obtained by droplet etching epitaxy show excellent performances, making the realization of these QDs into PICs highly appealing. Here, we show the first implementation in this direction, realizing the key passive elements needed in PICs, i.e., single-mode waveguides (WGs) with integrated GaAs-QDs and beamsplitters. We study the statistical distribution of wavelength, linewidth, and decay time of the excitonic line, as well as the quantum optical properties of individual emitters under resonant excitation. We achieve single-photon purities as high as 1 - g(2)(0) = 0.929 ± 0.009 and two-photon interference visibilities of up to VTPI = 0.953 ± 0.032 for consecutively emitted photons.

Measurement of the Bs0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}_s^0 $$\\end{document}→ μμ effective lifetime with the ATLAS detector

This paper reports the first ATLAS measurement of the Bs0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}_s^0 $$\\end{document}→ μμ effective lifetime. The measurement is based on the data collected in 2015–2016, amounting to 26.3 fb−1 of 13 TeV LHC proton-proton collisions. The proper decay-time distribution of 58 ± 13 background-subtracted signal candidates is fit with simulated signal templates parameterised as a function of the Bs0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}_s^0 $$\\end{document} effective lifetime, with statistical uncertainties extracted through a Neyman construction. The resulting effective measurement of the Bs0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}_s^0 $$\\end{document}→ μμ lifetime is 0.99−0.07+0.42\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {0.99}_{-0.07}^{+0.42} $$\\end{document} (stat.) ± 0.17 (syst.) ps and it is found to be consistent with the Standard Model.

Measurement of CP Violation in B^{0}→K_{S}^{0}π^{0} Decays at Belle II.

We report a measurement of the CP-violating parameters C and S in B^{0}→K_{S}^{0}π^{0} decays at Belle II using a sample of 387×10^{6} BB[over ¯] events recorded in e^{+}e^{-} collisions at a center-of-mass energy corresponding to the ϒ(4S) resonance. These parameters are determined by fitting the proper decay-time distribution of a sample of 415 signal events. We obtain C=-0.04_{-0.15}^{+0.14}±0.05 and S=0.75_{-0.23}^{+0.20}±0.04, where the first uncertainties are statistical and the second are systematic.

Temperature resolved decay time components of Mg4FGeO6:Mn using the maximum entropy method.

A thermographic phosphor's decay time distribution over its temperature-sensitive range was retrieved with the Maximum Entropy Method (MEM). A decay time distribution consists of a range of decay times, each with an associated weighting for the decay time component's prevalence in the analyzed decay curve. With the MEM, significant decay time contributions of a decay curve have high weighting and are therefore found as peaks in the decay time distribution, where the width and peak value are correlated with the relative weight of the decay time components. These peaks in the decay time distribution give increased insight into a phosphor's lifetime behavior, which often cannot accurately be represented by a single or even two decay time components. The changes in the location of peaks in the decay time distribution with temperature can be used for thermometry, and this method has the benefit of being less sensitive to the multi-exponentiality of phosphor decay than mono-exponential decay time fitting. The method also resolves the underlying decay components with no assumptions of the number of significant decay time components. Initially, when the decay time distribution of Mg4FGeO6:Mn was captured, the collected decay included decaying luminescence from the alumina oxide tube in the tube furnace. Therefore, a second calibration was performed where the luminescence from the alumina oxide tube was minimized. These two calibration datasets were used to demonstrate that the MEM could characterize decays from two separate sources simultaneously.

Photo‐Carrier Lifetime in Binary and Ternary Heterostructures of Transition Metal Dichalcogenides

Binary and ternary transition metal dichalcogenide (TMD) heterostructures, MSe2 and MSeS (where M = Mo or W), are investigated as future building blocks for high‐performance device applications with a tailorable electronic bandgap. For light‐emitting device applications, investigating the decay time of the material is a prerequisite. Herein, time‐resolved photoluminescence (TRPL) of binary and ternary TMD heterostructures is measured. A tri‐exponential function is adopted to fit the TRPL data. Short, medium, and long decay times are <50 ps, ≈400 ps, and >400 ps, respectively. Except for monolayer MoSe2 and MoSeS, only two PL decay time components are observed with a large contribution from short decay time photocarriers (>80%). Bilayer TMDs exhibit a much shorter PL decay time, which could be attributed to the indirect nature of excitons and different dielectric environments, compared with that of monolayer TMDs. Using the center‐of‐mass (CM) method, a PL decay time map is successfully obtained for binary and ternary TMD heterostructures. This allows the qualitative visualization of the decay time distribution within the heterostructure or among other materials. This technique could be applied to assess the decay time of materials used in high‐performance light‐emitting devices.

Laser excitation effects in lifetime-based high-speed phosphor thermometry

With high-speed phosphor thermometry becoming more established follows the need for an improved understanding of laser excitation induced measurement errors. With this aim in mind, the impact of kHz laser excitation on the lifetime method was investigated for the phosphors Mg3FGeO6:Mn (MFG) and YVO4:Tm. The results showed that significant measurement errors can occur for both phosphors. The Maximum Entropy Method (MEM) was utilized to observe changes in the distribution of decay time with changes in laser excitation fluence and repetition rate. In the light of this analysis, it was concluded that the changes in measured decay time and therefore measured temperature cannot be primarily attributed to laser heating for either phosphor. The dominant source of changes in the measured decay time is ascribed to changes in the distributions of decay time with laser fluence for YVO4:Tm and laser irradiance for MFG.

Development of a Bayesian estimation tool to determine the optimal duration of apixaban discontinuation before a high-bleeding risk procedure.

Apixaban is a direct oral anticoagulant (DOAC). Many studies have shown that it shows high pharmacokinetic interindividual and intraindividual variability (IIV). The risk of hemorrhage is a major concern for patients treated with apixaban to undergo an operation or an invasive procedure. Due to this large pharmacokinetic variability, the current recommendations concerning the optimal duration of apixaban discontinuation before a high-bleeding risk procedure concern the general population and not a specific patient. The aim of this study was (1) to investigate by simulation the distribution of decay time of apixaban concentration and (2) to develop and validate an easy-to-use web tool to estimate the individual decay time of apixaban in a "real-life" situation. A systematic review of the literature was conducted to select the relevant pharmacokinetic models for the creation of the web tool. For each model, pharmacokinetic profiles were simulated and the time to reach concentrations below the threshold of 30 ng/ml (T30) was calculated. One of the selected models was chosen to perform a Bayesian estimation and predict the optimal duration of apixaban discontinuation before a high-bleeding risk procedure. All these results were concatenated into the PrevBleed application developed with the R Shiny package.

A development of a compact software package for systematic error studies in muon $$g-2$$/EDM experiment at J-PARC

The J-PARC muon g-2/EDM experiment aims to measure the muon magnetic moment anomaly $a_{\mu} = (g -2 ) / 2 ~ $. The target sensitivity for $a_{\mu}$ is a statistical uncertainty of $450 \times 10^{-9}$, and $a_{\mu}$ can be extracted by measuring the spin precession of muons ($\omega_a$). The $\omega_a$ can be extracted from the distribution of muon decay time, and the time is measured by reconstructing tracks of positrons which are decayed from the muons. To extract $\omega_a$ precisely, the systematic effects on $\omega_a$ should be controlled under the aforementioned sensitivity. To study systematic effects, we develop a compact simulation package, and using our developed package, we study several systematic effects and discuss results. We discuss the package details and studies of systematic effects on $\omega_a$ based on our package.

Quantization of the mean decay time for non-Hermitian quantum systems

We show that the mean time, which a quantum particle needs to escape from a system to the environment, is quantized and independent from most dynamical details of the system. In particular, we consider a quantum system with a general Hermitian Hamiltonian $\hat{H}$ and one decay channel, through which probability dissipates to the environment with rate $\Gamma$. When the system is initially prepared exactly in the decay state, the mean decay time $\langle T \rangle$ is quantized and equal to $w/(2\Gamma)$. $w$ is the number of distinct energy levels, i.e. eigenvalues of $\hat{H}$, that have overlap with the decay state, and is also the winding number of a transform of the resolvent in the complex plane. Apart from the integer $w$, $\langle T \rangle$ is completely independent of the system's dynamics. The complete decay time distribution can be obtained from an electrostatic analogy and features rare events of very large dissipation times for parameter choices close to critical points, where $w$ changes, e.g. when a degeneracy is lifted. Experiments of insufficient observation time may thus measure a too small value of $w$. We discuss our findings in a disordered tight-binding model and in the two-level atom in a continuous-wave field.

Empirical Phase Calibration for Multistatic Specular Meteor Radars Using a Beamforming Approach

AbstractSpecular meteor radars have proven useful for observing mesosphere and lower thermosphere altitudes. More recently, their capabilities have been enhanced by including multistatic configurations. In both cases, monostatic and multistatic, the multiantenna interferometer used to determine the location of the measurements needs to be carefully calibrated in phase. In this work we proposed a technique to calibrate the receiving phases of such interferometers, including the standard five‐antenna Jones configuration located on a plane and arbitrary configurations not necessarily located on a plane and not limited to five antennas. Our technique uses beamforming and nonlinear least squares fitting to determine the angle of arrivals that are consistent with the complex spatial coherences of the detected meteors. The optimization process uses a priori information based on the expected angular and altitude distribution of the echoes. The technique is demonstrated using real bistatic data. The obtained distribution of inverse decay time as a function of altitude is shown to be a sensitive and independent quality control feature of the applied calibration.

Seasonal variations in vertical distribution of meteor decay time as observed from meteor radars at 8.5°N and 80°N

The decay times of meteor radar echoes have been used for decades to investigate characteristics of the mesosphere and lower thermosphere (MLT) region. As the meteor echo decay time depends on background atmospheric parameters, in the present communication, we examine the seasonal variation of the vertical distributions of underdense meteor echo decay times with respect to echo strength. Observations from two similar radars located at two distinct geographical locations, Thumba (8.5°N, 77°E) and Eureka (80°N, 85.8°W) were used for the present study. Here, the radar received signal power is categorized into strong and weak echoes and vertical profiles of their decay times are constructed. It has been noticed that the monthly mean decay time vertical profile turning altitude (i.e., inflection point) varies in the range of 80–87 km of altitude depending on latitude. The turning altitude is observed at relatively lower heights in the winter than in summer at both the latitudes. The present analysis shows that the meteor decay time below the mean turning altitude follows a decreasing trend with decreasing altitude, which is quite distinct to the behaviour of ambipolar diffusion. It is also observed that there is a difference in mean decay time of strong and weak echoes below 90 km of altitude, which is very prominently seen at lower altitudes. This difference shows a seasonal pattern at high latitude, but does not show any seasonal variation at low latitude. The present results are discussed in light of current understanding of the meteor decay time.

Bootstrapping reliable noise measure in time-gated nuclear magnetic resonance data

Time gating is a commonly used approach in the pre-processing of nuclear magnetic resonance (NMR) data before Laplace inversion. Gating suppresses spurious signals that can degrade recovered decay time distributions and therefore often stabilizes inversion. However, care must be taken in applying this technique to real world data where both non-Gaussian and correlated noise decrease the efficacy of noise reduction through stacking. If not properly accounted for, unreliable noise estimates introduce inversion artefacts. Fortunately, noise realization proxies obtained through data phasing can be used to bootstrap reliable confidence intervals for the windowed data. Benefits of the approach are demonstrated through inversion of synthetics as well as borehole data from a deep carbon capture and sequestration application. We also introduce an open source cross platform data processing utility with these capabilities which interested persons can use to explore the impacts of various processing workflows.

Reliable noise measure in time-gated NMR data

Summary Time gating is a commonly used approach in the pre-processing of nuclear magnetic resonance data before inversion. Gating suppresses spurious signals that can degrade recovered decay time distributions and therefore often stabilizes inversion. However, care must be taken in applying this technique when assumptions of uncorrelated Gaussianity break down and reduce stacking efficiency. If not properly accounted for, unreliable noise estimates introduce inversion artefacts through over- or underfitting of the data. Block-bootstrap resampling of noise realization proxies obtained through data phasing can be used to generate reliable noise estimates for the windows. Benefits of the approach are demonstrated through inversion of synthetic and borehole data. Analysis confirms that bootstrapped noise metrics are more reliable under variable noise conditions and result in more stable inversion results.

Electrowetting on dielectric: experimental and model study of oil conductivity on rupture voltage

Electrowetting on dielectric devices uses a conducting (water) and insulating (oil) liquid phase in conjunction on a dielectric layer. In these devices, the wetting properties of the liquid phases can be manipulated by applying an electric field. The electric field can rupture the initially flat oil film and promotes further dewetting of the oil. Here, we investigate a problem in the operation of electrowetting on dielectric caused by a finite conductivity of the oil. In particular, we find that the voltage at which the oil film ruptures is sensitive to the application of relatively low DC voltages prior to switching. Here, we systematically investigate this dependence using controlled driving schemes. The mechanism behind these history effects point to charge transport processes in the dielectric and the oil, which can be modeled and characterized by a decay time. To quantify the effects the typical response timescales have been measured with a high-speed video camera. The results have been reproduced in simulations. In addition, a simplified yet accurate equivalent circuit model is developed to analyze larger data sets more conveniently. The experimental data support the hypothesis that each pixel can be characterized by a single decay time. We studied an ensemble of pixels and found that they showed a rather broad distribution of decay times with an average value of about 440 ms. This decay time can be interpreted as a discharge timescale of the oil, not to be confused with discharge of the entire system which is generally much faster (<1 ms). Through the equivalent circuit model, we also found that variations in the fluoropolymer (FP) conductivity cannot explain the distribution of decay times, while variations in oil conductivity can.

Oxidation Mechanism of Si1-xGex Nanowires with Au Catalyst Tip as a Function of Ge Content.

Si1-xGex nanowires (NWs) (0.22 ≤ x ≤ 0.78) were synthesized using a vapor-liquid-solid procedure with a Au catalyst. We measured the intrinsic physical, chemical, and electrical properties of the oxidized Si1-xGex NWs using several techniques, including transmission electron microscopy, X-ray photoemission spectroscopy, and optical pump-THz probe spectroscopy. We suggest two distinct oxidation mechanisms depending on the Ge content in the Si1-xGex NWs: (i) when the Ge content is around 0.22, a Au catalytic effect brings about oxidation in both the axial and lateral directions; and (ii) when the Ge content is greater than 0.22, the Au tip is detached from the NW body and does not act as a catalyst, which is a result of the high degree of Ge-atom participation in the oxidation process. Additionally, we measured the photoconductivity decay time distribution for the Si1-xGex NWs before and after oxidation process; the decay time is significantly shortened in oxidized Si1-xGex NWs (0.22 < x), whereas it is maintained for Si-rich Si1-xGex NWs (x ≈ 0.22) as compared to the as-grown Si1-xGex NWs. It indicates that the number of defect states is generated with the formation of defective Ge oxide at the oxide-shell-layer/Si1-xGex-core-NW interface.

Effects of urban street spatial parameters on sound propagation

Many studies have demonstrated that the effect of urban street spatial shape on sound propagation cannot be ignored. Most previous studies are based on idealised spatial models and but not systematically and comprehensively examine the real and complex street space. This paper takes the actual streets of a high-density city as research objects, select reliable spatial parameters, obtain the acoustic propagation data using computer simulation, identify the sound propagation characteristics and establish sound propagation models of urban streets. In total, 144 samples have been tested, 13 spatial parameters, including the width information, height information, section information and plan information of streets, have been selected, and three acoustic indices, which include the sound attenuation, reverberation time and early decay time, have been analysed in this paper. The sound propagation in the urban street is consistent with the propagation characteristics of the semi-free sound field, i.e. the sound attenuation is linearly correlated with the logarithm of the sound propagation distance. This linear correlation becomes more pronounced for the greater Plan enclosure degree and more even distribution of façades. The trend of sound attenuations decreases with the increasing Cross-sectional enclosure degree, increasing Plan enclosure degree in the Near Zone or decreasing Vehicle lane width. Reverberation time is primarily distributed between 1.0 s and 3.0 s and tends to be stable when the propagation distance increases. The mean reverberation time increases with the increasing Mean façade height, Sidewalk width, Cross-sectional enclosure degree in the Near Zone or Standard deviation of Plan enclosure degree in the Near Zone. The typical early decay time distribution curve is clearly divided into two areas along the propagation direction. In the first area, the early decay time value is notably small and nearly equals zero. With a sudden increase, the early decay time maintains at a relatively stable value in the second area (stable area) of 0 to 3.0 s. The mean early decay time in the stable area increases with the increasing Vehicle lane width, increasing Cross-sectional enclosure degree or decreasing Standard deviation of Plan enclosure degree in the Near Zone.

Luminescence of pyrazolic 1,3-diketone [formula omitted] complex with 1,10-phenanthroline

We studied luminescent properties of Pr3+ complex with pyrazole and 1, 10-phenanthroline ligand environment. It was demonstrated that the complex exhibits so-called “antenna” effect which involves the electronic excitation transfer from the ligands to the rare-earth ion. The observed complex structure of the luminescence spectrum specific to Pr3+ indicates that in the investigated compounds the luminescence originates from the rare-earth ion exclusively. The obtained data provided a means to identify the electronic transitions in the ion and to develop the corresponding energy diagram. Fluorescence lifetime imaging revealed uniform distribution of luminescence decay times for the Pr3+ complex crystalline phase. Consequently, the Pr3+ complex under study has one type of emission sites.

InGaN/GaN light-emitting diode having direct hole injection plugs and its high-current operation.

The light-emitting diode (LED) with an improved hole injection and straightforward process integration is proposed. p-type GaN direct hole injection plugs (DHIPs) are formed on locally etched multiple-quantum wells (MQWs) by epitaxial lateral overgrowth (ELO) method. We confirm that the optical output power is increased up to 23.2% at an operating current density of 100 A/cm2. Furthermore, in order to identify the origin of improvement in optical performance, the transient light decay time and light intensity distribution characteristics were analyzed on the DHIP LED devices. Through the calculation of the electroluminescence (EL) decay time, internal quantum efficiency (IQE) is extracted along with the recombination parameters, which reveals that the DHIPs have a significant effect on enhancement of radiative recombination and reduction of efficiency droop. Furthermore, the mapping PL reveals that the DHIP LED also has a potential to improve the light extraction efficiency by hexagonal pyramid shaped DHIPs.