Decay Mechanism Research Articles

Daylighting performance assessment of traditional skywell dwellings: A case study in Fujian, China

China's rural revitalization strategy has aroused people's attention toward the preservation and renewal of traditional dwellings. Characterized by small courtyards and small top openings, traditional skywell dwellings in southern China are facing prominent daylight environment problems. However, only few studies have evaluated the visual comfort in skywell dwellings under daylight conditions using incomprehensive methods. To fill this gap, this paper systematically assessed the daylighting performance of skywell dwellings in Xingxian Village from 2D reference planes and 3D spatial interfaces. An accurate daylighting simulation model of skywell dwellings was established and validated with field measurements. ClimateStudio was used to analyze the performance metrics from the aspects of daylight quantity, daylight uniformity, and glare. Results identify insufficient daylight quantity indoors as the severest problem in skywell dwellings, which require artificial lighting throughout almost the entire daytime. Seasonal glare and inferior daylight uniformity were also observed in semi-outdoor areas. The effects of top, horizontal, and vertical spatial interfaces on the daylight environment were further investigated, and results highlight the influence of roof slope and opening setting on indoor lighting, the decay mechanism of daylight quantity on horizontal substrate interfaces, and the mismatch between daylight distribution and the positions of doors and windows on vertical enclosure interfaces. The changes in building orientation and seasons were also found to have limited effects on daylighting performance. These results can guide architects specializing in dwelling renovation, so as to improve the visual comfort of buildings and save up on living and energy costs due to artificial lighting.

Light quark decays of doubly heavy baryons in light front approach

We explore the semileptonic and nonleptonic decays of doubly heavy baryons (Omega _{cc}^{(*)+},Omega _{bb}^{(*)0},Omega _{bc}^{(*)-},Omega _{bc}^{prime 0}) induced by the srightarrow u transition. Hadronic form factors are parametrized by transition matrix elements and are calculated in the light front quark model. With the form factors, we make use of helicity amplitudes and analyze semileptonic and nonleptonic decay modes of doubly heavy baryons. Benchmark results for partial decay widths, branching fractions, forward–backward asymmetries and other phenomenological observables are derived. We find that typical branching fractions for semileptonic decays into ell bar{nu } are at the order 10^{-7}-10^{-8} and the ones for nonleptonic decays are at the order 10^{-5}, which are likely detectable such as in LHCb experiment. With the potential data accumulated in future, our results may help to shape our understanding of the decay mechanism in the presence of two heavy quarks.

Energy transfer of the solar wind turbulence based on Parker solar probe and other spacecraft observations

The supersonic solar wind, first predicted by Parker and then observed by Mariners, extends to form a heliosphere around the Sun. The energy supply from the energy containing range, the energy cascade though the inertial range, and the eventual energy dissipation are three basic processes of the energy transfer in the solar wind and have been studied for a long time. However, some basic issues remain to be discovered. Here, we review the recent progress in the mechanisms of energy transfer of the solar wind turbulence from the observational perspective. Based on the Parker solar probe observations, the energy supply mechanism by the low-frequency break sweeping is proposed to provide enough energy for the proton heating in the slow solar wind. This mechanism also works in the fast solar wind. The energy flux by the low-frequency break sweeping is consistent with that by the classical von Kármán decay mechanism. For the energy cascade in the inertial range, the scaling behavior of the third-order structure functions demonstrates the effect of the complex dynamics of the solar wind. The process of energy transfer is fundamental to understand the solar wind turbulence and help to construct the model of the space environment.

Extended R-matrix description of two-proton radioactivity

Two-proton (2p) radioactivity provides fundamental knowledge on the three-body decay mechanism and the residual nuclear interaction. In this work, we propose decay width formulae in the extended R-matrix framework for different decay mechanisms, including sequential 2p decay, diproton decay, tri-body decay, and sequential two-diproton decay. The diproton and tri-body formulae, combined with information on the two-nucleon transfer amplitude and Wigner single-particle reduced width, can reproduce well experimental 2p radioactivity half-lives. For the case of 67Kr, theoretical predictions for direct 2p decay give much larger half-lives than the recent measurement from RIKEN. A combination of direct and sequential 2p emission is analyzed by considering a small negative one-proton separation energy and a possible enhanced contribution from the p-wave component. The present method predicts that 71Sr and 74Zr may be the most promising candidates for future study on 2p radioactivity. Our model gives an upper limit of 55(4) keV for the decay width of 4p emission in recently found four-proton resonant nuclide, 18Mg, which agrees with the observed width of 115(100) keV.

Accelerating defect analysis of solar cells via machine learning of the modulated transient photovoltage

Fast and non-destructive analysis of material defect is a crucial demand for semiconductor devices. Herein, we are devoted to exploring a solar-cell defect analysis method based on machine learning of the modulated transient photovoltage (m-TPV) measurement. The perturbation photovoltage generation and decay mechanism of the solar cell is firstly clarified for this study. High-throughput electrical transient simulations are further carried out to establish a database containing millions of m-TPV curves. This database is subsequently used to train an artificial neural network to correlate the m-TPV and defect properties of the perovskite solar cell. A Back Propagation neural network has been screened out and applied to provide a multiple parameter defect analysis of the cell. This analysis reveals that in a practical solar cell, compared to the defect density the charge capturing cross-section plays a more critical role in influencing the charge recombination properties. We believe this defect analysis approach will play a more important and diverse role for solar cell studies.

Frequency dependent decay of water waves due to floating balls with application to simulating wave decay in the marginal ice zone

An experimental study is conducted to investigate the frequency dependent decay of free-surface water waves in a sloshing tank with partially-submerged floating plastic balls on the free-surface. The present study is motivated by the need to understand the possible mechanisms for ocean wave decay in the marginal ice zone. Laboratory experiments are performed to estimate the wave decay rate due to floating balls representing ice floes. The decay rates with the balls are sufficiently greater than the decay rates without the balls and we assume the effect of the balls dominates the decay. The temporal decay rates of the free-surface wave amplitudes are measured for a small excitation amplitude and different water-depths. The decay rates for the first and third modes of sloshing are extracted, even when these two modes are combined. It is shown that the decay rates obtained from the present study match with the exponent three power-law dependence on wave frequency as observed for the decay rates in the marginal ice zone. This matching of exponent suggests that the same mechanism may be responsible for both types of decay.

Nuclear pair electron spin echo envelope modulation

The interaction of electron spins with homonuclear spin pairs in their vicinity is one of the dominating mechanisms of electron spin echo decay at low temperature and low concentration. Here, we study this mechanism using established concepts of electron spin echo envelope modulation (ESEEM). We obtain analytical expressions for the Hahn echo, the refocused echo, the stimulated echo, and Carr–Purcell pulse trains with small numbers of π pulses. Hahn echo decay is well approximated by the product of nuclear pair ESEEM functions. The same approximation can explain dependence of stimulated echo decay on the first interpulse delay and provides reasonable time scale estimates for decay of Carr–Purcell echos after an odd number of π pulses. Carr–Purcell echoes after an even number of π pulses are rather sensitive to correlations within larger nuclear spin clusters. Approximations improve for both odd and even numbers of π pulses by factorising the nuclear spin bath into disjoint clusters, provided that modulation due to pairs of spins belonging to different clusters is considered in addition to cluster modulation. The analytical ESEEM expressions for the Hahn echo and the Carr–Purcell echo after two π pulses have the same mathematical form as the filter functions of these sequences of spin noise spectroscopy. This coincidence provides a computationally very efficient way of predicting Hahn echo decay induced by homonuclear spin pairs. The analytical pair product approximation predicts the previously observed (Bahrenberg et al., 2021) increase of the refocused echo amplitude when one refocusing time is incremented and other one is fixed but longer. In contrast, the spin-noise concept fails to predict this effect.

Evolution of optical phonon modes and thermoelectric properties in doped Bi2Te3 : A temperature-dependent Raman spectroscopy study

Due to its three-dimensional bulk-insulating nature and better room-temperature thermoelectric properties, ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ is widely explored as potential thermoelectric material and topological insulator. Here, we report the effect of smaller atoms (Ge, Se) doping on the evolution of the temperature-dependent optical phonon modes in polycrystalline single-phase ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$. While undoped ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ exhibits crystal inversion symmetry lowering in the investigated temperature range, the doped ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ retains the inversion symmetry below 270 K. As a result, the IR-active ${A}_{1u}^{2}$ phonon mode, which arises due to the lowering of crystal inversion symmetry, disappears in the doped ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ below 270 K. The increase in the full width at half maxima of Raman peaks and reduction in the phonon lifetime with an increase in temperature confirm the optical phonon decay in doped ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$, and hence lattice thermal conductivity is expected to decrease at higher temperatures. The lattice thermal conductivity estimated from the optical phonon modes is in line with the experimentally measured value, which affirms that optical phonon vibrations dominate the lattice thermal conductivity of ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$. At low temperature, the Ge-Se codoped ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ shows a fourfold enhancement of the Seebeck coefficient compared to that of undoped ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$. Our results give an insight into the optical phonon decay mechanism in the doped ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ and corroborate that optical phonons play a vital role in the lattice thermal conductivity of polycrystalline ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$. Also, it is found that Se-Ge codoped ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ can be used as an efficient near-room temperature thermoelectric material.

Timelike electromagnetic kaon form factor

We compute the electromagnetic charged kaon form factor in the timelike region by employing a Poincar\'e covariant formalism of the Bethe-Salpeter equation to study quark-antiquark bound states in conjunction with the Schwinger-Dyson equation for the quark propagator. Following a recent kindred calculation of the timelike electromagnetic pion form factor, we include the most relevant intermediate composite particles permitted by their quantum numbers in the interaction kernel to allow for a decay mechanism for the resonances involved. This term augments the usual gluon mediated interaction between quarks. For a sufficiently low energy timelike probing photon, the electromagnetic form factor is saturated by the $\ensuremath{\rho}(770)$ and $\ensuremath{\phi}(1020)$ resonances. We assume $SU(2)$ isospin symmetry throughout. Our results for the absolute value squared of the electromagnetic form factor agree qualitatively rather well and quantitatively moderately so with available experimental data.

A novel non-sense variant in the OFD1 gene caused Joubert syndrome.

Background: Joubert syndrome (JBS) is a rare neurodevelopmental disorder associated with progressive renal, liver, and retinal involvement that exhibits heterogeneity in both clinical manifestations and genetic etiology. Therefore, it is difficult to make a definite prenatal diagnosis. Methods: Whole-exome sequencing and Sanger sequencing were performed to screen the causative gene variants in a suspected JBS family. RNA-seq and protein model prediction were performed to clarify the potential pathogenic mechanism. A more comprehensive review of previously reported cases with OFD1 variants is presented and may help to establish a genotype-phenotype. Results: We identified a novel non-sense variant in the OFD1 gene, OFD1 (NM_003611.3): c.2848A>T (p.Lys950Ter). Sanger sequencing confirmed cosegregation among this family. RNA-seq confirmed that partial degradation of mutant transcripts, which was predicted to be caused by the non-sense-mediated mRNA decay (NMD) mechanism, may explain the reduction in the proportion of mutant transcripts. Protein structure prediction of the non-sense variant transcript revealed that this variant may lead to a change in the OFD1 protein structure. Conclusion: The genetic variation spectrum of JBS10 caused by OFD1 was broadened. The novel variants further deepened our insight into the molecular mechanism of the disease.

Effect of hydrogen atoms on potassium-ion electrets used in vibration-powered generators

Potassium-ion electrets, which are mainly composed of amorphous silica and potassium atoms, can accumulate negative charges and are expected to be useful for future vibration powered generators. According to previous research, the origin of the accumulation of negative charges was revealed to be related to the presence of SiO5 structures in amorphous silica. In general, Si–O bonds are so stable that potassium-ion electrets are expected to retain a high electric potential longer than previously studied materials and are therefore being studied intensively for practical use. However, charge decay phenomena were observed in previous experiments, and this presents serious problems. In this study, we focus on the role of hydrogen which is considered to be one of the origins of charge decay and have investigated the behavior of hydrogen in potassium-ion electrets and the mechanism of the charge decay using first-principles calculations. As a result, we found that hydrogen atoms can create a positively charged characteristic local structure or break SiO5 structures and therefore cause degradation of the negative charge storing ability of potassium-ion electrets.

Biocontrol activity of Bacillus halotolerans strain Pl7 against Botryosphaeria dothidea causing apple postharvest decay and potential mechanisms.

Apple ring rot, one of the most common apple postharvest diseases during storage, is caused by Botryosphaeria dothidea. Fungicide application is the most widely used method to control this disease, but the increasing environmental and food safety concerns greatly limit their use. The present study aimed to examine the biocontrol activity and underlying action mechanism of Bacillus halotolerans strain Pl7 against B. dothidea. The results revealed that B. halotolerans strain Pl7 exhibited strong inhibitory activity against B. dothidea by 69% in vitro. The culture filtrate of strain Pl7 possessed cellulase, β-1, 3-glucanase, protease activity and mediated the antifungal activity against B. dothidea. Further analysis demonstrated that culture filtrate of strain Pl7 could cause cell membrane permeabilization of B. dothidea. Apple fruit suffering from ring rot induced by a carbendazim (CBZ)-sensitive or -resistant B. dothidea isolate was much suppressed after being treated with strain Pl7, maintaining postharvest quality. The ability of strain Pl7 to swiftly colonize and thrive in apple fruit wounds was demonstrated by a re-isolation assay. Additional transcriptome studies of untreated and treated apple fruit with strain Pl7 revealed that strain Pl7 mostly changed the expression of genes functioning in plant secondary metabolite biosynthesis and plant-pathogen interaction. In light of these outcomes, the underlying antagonistic mechanism was investigated, and B. halotolerans strain Pl7 was identified as a promsing microbial biocontrol agent against apple postharvest decay.

Quantum mechanics/molecular mechanics studies on the excited-state decay mechanisms of cytidine aza-analogues: 5-azacytidine and 2'-deoxy-5-azacytidine in aqueous solution.

The excited state properties and deactivation pathways of two DNA methylation inhibitors, i.e., 5-azacytidine (5ACyd) and 2'-deoxy-5-azacytidine (5AdCyd) in aqueous solution, are comprehensively explored with the QM(CASPT2//CASSCF)/MM protocol. We systematically map the feasible decay mechanisms based on the obtained excited-state decay paths involving all the identified minimum-energy structures, conical intersections, and crossing points driving the different internal conversion (IC) and intersystem crossing (ISC) routes in and between the 1ππ*, 1nπ*, 3ππ*, 3nπ*, and S0 states. Unlike the 1nπ* state below the 1ππ* state in 5ACyd, deoxyribose group substitution at the N1 position leads to the 1ππ* state becoming the S1 state in 5AdCyd. In 5ACyd and 5AdCyd, the initially populated 1ππ* state mainly deactivates to the S0 state through the direct 1ππ* → S0 IC or mediated by the 1nπ* state. The former nearly barrierless IC channel of 1ππ* → S0 occurs ultrafast via the nearby low-lying 1ππ*/S0 conical intersection. In the latter IC channel of 1ππ* → 1nπ* → S0, the initially photoexcited 1ππ* state first approaches the nearby S2/S1 conical section 1ππ*/1nπ* and then undergoes efficient IC to the 1nπ* state, followed by the further IC to the initial S0 state via the S1/S0 conical intersection 1nπ*/S0. The 1nπ*/S0 conical intersection is estimated to be located 6.0 and 4.9 kcal mol-1 above the 1nπ* state minimum in 5ACyd and 5AdCyd, respectively, at the QM(CASPT2)/MM level. In addition to the efficient singlet-mediated IC channels, the minor ISC routes would populate 1ππ* to T1(ππ*) through 1ππ* → T1 or 1ππ* → 1nπ* → T1. Relatively, the 1ππ* → 1nπ* → T1 route benefits from the spin-orbit coupling (SOC) of 1nπ*/3ππ* of 8.7 cm-1 in 5ACyd and 10.2 cm-1 in 5AdCyd, respectively. Subsequently, the T1 system will approach the nearby T1/S0 crossing point 3ππ*/S0 driving it back to the S0 state. Given the 3ππ*/S0 crossing point located above the T1 minimum and the small T1/S0 SOC, i.e., 8.4 kcal mol-1 and 2.1 cm-1 in 5ACyd and 6.8 kcal mol-1 and 1.9 cm-1 in 5AdCyd, respectively, the slow T1 → S0 would trap the system in the T1 state for a while. The present work could contribute to understanding the mechanistic photophysics and photochemistry of similar aza-nucleosides and their derivatives.

Fast intersystem crossing in the tetracene dimers as a source of “dark” state

Tetracene (Tc) is a prototype material undergoing singlet fission (SF), the formation of a pair of triplet excitons from a singlet exciton. The tetracene dimer Tc2 is supposed to be a structural unit providing SF behavior. This work is devoted to the study of the mechanism of singlet exciton decay in van der Waals dimers of Tc2. A nanosecond pump-probe approach is used, tuning both pumping and probing wavelengths. It is shown that the photoexcitation of both the Tc monomer and dimer gives rise to a triplet Tc(T1) with very similar photoionization spectra, indicating an intersystem crossing (ISC) as the source of Tc(T1) in both cases. This finding, together with the very short lifetime of the singlet exciton in van der Waals Tc2 dimers as reported earlier in the literature, indicates that the ISC process is much faster in the dimer than in bare Tc. The factors that increase the rate of ISC in donor–acceptor complexes are the low-lying charge-transfer state in the Tc2 dimer and the proximity in the energy between the singlet S1 and triplet T2 states in tetracene. This fast ISC process is assigned to the temperature-independent process reported earlier in the literature, leading to a “dark” state in tetracene. The results obtained indicate that the dimer of tetracene can be considered to be a structural unit responsible for both fast ISC and SF processes.

Probing the degradation of LiCoO2 in batteries subjected to high-voltage cycling with 17O solid-state NMR spectroscopy.

The long-term cycling stability of LiCoO2 under high-voltage operation in lithium-ion batteries is still not satisfactory and the mechanism of capacity decay is not well understood. Here we mainly apply 17O MAS NMR spectroscopy to probe the phase transformation of cycled LiCoO2 cathodes in both liquid cells and solid cells. It turns out that deterioration into the spinel phase is the main cause.

Molecular Nature of X(3872) in B 0 → K 0 X(3872) and B + K + X(3872) Decays

We investigate the decays of B 0 → K 0 X(3872) and B + → K + X(3872) based on the picture where the X(3872) resonance is strongly coupled to the channel. In addition to the decay mechanism where the X(3872) resonance is formed from the pair hadronization with the short-distance interaction, we have also considered the rescattering diagrams in the long-distance scale, where D and are formed from c and separately. Because of the difference of the mass thresholds of charged and neutral channels, and the rather narrow width of the X(3872) resonance, at the X(3872) mass, the loop functions of and are much different. Taking this difference into account, the ratio of can be naturally obtained. Based on this result, we also evaluate the decay widths of . It is expected that future experimental measurements of these decays can be used to elucidate the nature of the X(3872) resonance.

Identification of the Decay Pathway of Photoexcited Nucleobases

The identification of the decay pathway of the nucleobase uracil after being photoexcited by ultraviolet light has been a long-standing problem. Various theoretical models have been proposed but yet to be verified. Here, we propose an experimental scheme to test the theoretical models of gas phase uracil decay mechanism by a combination of ultrafast x-ray spectroscopy, x-ray diffraction, and electron diffraction methods. Incorporating the signatures of multiple probing methods, we demonstrate an approach that can identify the dominant mechanism of the geometric and electronic relaxation of the photoexcited uracil molecule among several candidate models.

Photophysics of the red-form Kaede chromophore.

The green fluorescent protein (GFP) drove revolutionary progress in bioimaging. Photoconvertible fluorescent proteins (PCFPs) are an important branch of the FP family, of which Kaede is the prototype. Uniquely, PCFPs can be permanently switched from green to red emitting forms on UV irradiation, facilitating applications in site-specific photolabelling and protein tracking. Optimisation and exploitation of FPs requires understanding of the photophysical and photochemical behaviour of the chromophore. Accordingly, the principal GFP chromophore has been the subject of intense experimental and theoretical investigation. In contrast, the photophysics of the red emitting PCFP chromophore are largely unstudied. Here we present a detailed investigation of the excited-state properties of the Kaede chromophore in solution, utilising steady state measurements, ultrafast time-resolved electronic and vibrational spectroscopies, and electronic structure theory. Its excited state dynamics are very different to those of the parent GFP. Most remarkably, the PCFP chromophore has highly complex wavelength-dependent fluorescence decays and a mean lifetime an order of magnitude longer than the GFP chromophore. Transient electronic and vibrational spectroscopies suggest that these dynamics arise from a range of excited-state conformers that are spectrally and kinetically distinct but chemically similar. These conformers are populated directly by excitation of a broad thermal distribution of ground state structures about a single conformer, suggesting an excited-state potential surface with several minima. Temperature-dependence confirms the existence of barriers on the excited-state surface and reveals the radiationless decay mechanism to be internal conversion. These experimental observations are consistent with a model assuming a simple ground state potential energy surface accessing a complex excited state possessing multiple minima.

Ultrafast time-resolved carrier dynamics in tellurium nanowires using optical pump terahertz probe spectroscopy.

We report carrier relaxation dynamics in semiconducting tellurium nanowires (average diameter ∼ 10 nm) using ultrafast time-resolved terahertz spectroscopy. After photoexcitation using an 800 nm pump pulse, we observed an initial increase in the THz conductivity due to the absorption of THz radiation by photoexcited carriers. The time evolution of the differential conductivity (Δσ(τpp) = σpump on(τpp) - σpump off) shows a bi-exponential relaxation with the initial fast decay time scale of τ1 ∼ 25 ps followed by a longer relaxation time constant of τ2 ∼ 100 ps. Interestingly, the two time scales depend on the amount of the capping agent present on the surface of TeNWs, showing a faster relaxation of the photoexcited carriers as the percentage of capping decreases. This is physically interpreted as the surface state mediated relaxation mechanism of the photo-pumped carriers depending on the density of available surface states. A quantitative understanding is obtained using a coupled rate equation model taking into account the decay mechanisms determined from the surface mediated relaxation rate (DS) and direct recombination rate (DR) of the electron-hole pairs. Furthermore, the measured lattice temperature (TL) dependent dynamics, showing a faster relaxation at lower temperature, is understood using the same rate equation model, giving a power law dependence of the electron-hole recombination rate (DR) on TL as DR ∝ TL-1/2. This is explained by estimating DR using the van Roosbroeck-Shockley theory taking into account the density of states () of one-dimensional nanowires. Furthermore, to understand the measured frequency-dependent THz photoconductivity, we model Δσ(ω) using the Boltzmann transport equation taking into account the energy-dependent scattering rates showing the dominant role of short range (Γsr) and Coulomb scattering (ΓC) rates in the relaxation process, which further provides a measure of the charged and neutral impurity concentrations.

α -particle formation and clustering in nuclei

The nucleonic localization function has been used for a decade to study the formation of $\ensuremath{\alpha}$ particles in nuclei, by providing a measure of having nucleons of a given spin in a single place. However, differences in interpretation remain, compared to the nucleonic density of the nucleus. In order to better understand the respective role of the nucleonic localization function and the densities in the $\ensuremath{\alpha}$-particle formation in cluster states or in the $\ensuremath{\alpha}$-decay mechanism, both an analytic approximation and microscopic calculations, using energy density functionals, are undertaken. The nucleonic localization function is shown to measure the anticentrifugal effect, and is not sensitive to the level of compactness of the $\ensuremath{\alpha}$ particle itself. It probes the purity of the spatial overlap of four nucleons in the four possible (spin, isospin) states. The density provides, in addition, information on the compactness of an $\ensuremath{\alpha}$-particle cluster. The respective roles of the nucleonic localization function and the density are also analyzed in the case of $\ensuremath{\alpha}$ particle emission. More generally, criteria to assess the prediction of $\ensuremath{\alpha}$ cluster in nuclear states are provided.