Gradual Decay Research Articles

Calculation and application research on real-time source term diffusion in NPP auxiliary building under accident circumstances

Abstract In the light of radioactive material leakage (due to containment bypass or failure) to the auxiliary building and its service compartments under severe accident circumstances, key techniques related to accident source terms in the nuclear emergency building were researched. During the research, the source-term diffusion and migration patterns were simulated in the building compartments, including the simulation of the gradual diffusion and decay process (driven by circulating air) of fission-derived gases and aerosol toward each compartment. Besides that, by taking a M310 unit at Fangjiashan NPP as the application object, the scenarios of initial accidents of LB/MB/SB-LOCA, MSLB and SGTR were chosen to establish a real-time diffusion calculation model for in-building radioactive source terms under nuclear accident circumstances. While considering the circumstances before and after being intervened by accident mitigation measures, the concentration distribution of radionuclides in the auxiliary building and personnel total-exposure radiation dose rate were quickly assessed online, and a basis was provided for the visualization of radiation dosage and the assessment of received radiation dosage and injury & death hazards during personnel activities outside the main control room.

Primordial magnetogenesis in a bouncing model with dark energy

We investigate primordial magnetogenesis within a quantum bouncing model driven by a scalar field, focusing on various non-minimal couplings between the electromagnetic field and the scalar field. We test three cases: no coupling, a Cauchy coupling with gradual decay, and a Gaussian coupling with rapid fall-off. By exploring these scenarios, we assess a wide range of coupling strengths across different scales. The scalar field, with an exponential potential, behaves as pressureless matter in the asymptotic past of the contracting phase, as stiff matter around the bounce, and as dark energy during the expanding phase. Our findings reveal that, among the tested cases, only the Gaussian coupling can explain the generation of primordial magnetic fields on cosmological scales.

The propagation characteristics of a detonation wave in uniformly premixed gases within a semi-confined channel

Based on the OpenFOAM platform, a numerical study was conducted to investigate the propagation characteristics of a detonation wave in uniformly premixed gases within a semi-confined channel, specifically examining the changes in wave's structure and analyzing the detonation reinitiation-extinguishment process. The results indicate that, due to the weak confinement, the detonation wave experiences lateral expansion, with transverse waves on the detonation wave front penetrating into the inert gas and forming segmented protrusions on the oblique shock wave. During the propagation process, the number of transverse waves decreases gradually, and the reflected waves formed by the interaction between transverse waves and the inert gas are weak, collectively leading to a gradual decay in the strength of the detonation wave and a reduction in the frequency of pressure oscillation on the detonation wave front. Furthermore, when transverse waves interact with the inert gas and undergo Mach reflection, the reflected waves would detach the inert gas and form new transverse waves promoted by upward-moving old transverse waves and disturbances on the flame front, thereby extending the duration distance of the detonation wave. Subsequently, after the detonation wave decouples, a transverse wave reflected from the inert gas interface interacts with the lower wall, triggering local detonation reinitiation, which generates a higher-intensity longitudinal wave that couples with the leading shock wave, temporarily restoring the detonation wave and forming lateral detonation in the decoupled region. However, the detonation wave will ultimately extinguish due to the attenuation of transverse waves' intensity and decreasing number of these waves.

Electrostatic Preorganization in Three Distinct Heterogeneous Proteasome β-Subunits.

The origin of the enzyme's powerful role in accelerating chemical reactions is one of the most critical and still widely discussed questions. It is already accepted that enzymes impose an electrostatic field onto their substrates by adopting complex three-dimensional structures; therefore, the preorganization of electric fields inside protein active sites has been proposed as a crucial contributor to catalytic mechanisms and rate constant enhancement. In this work, we focus on three catalytically active β-subunits of 20S proteasomes with low sequence identity (∼30%) whose active sites, although situated in an electrostatically miscellaneous environment, catalyze the same chemical reaction with similar catalytic efficiency. Our in silico experiments reproduce the experimentally observed equivalent reactivity of the three sites and show that obliteration of the electrostatic potential in all active sites would deprive the enzymes of their catalytic power by slowing down the chemical process by a factor of 1035. To regain enzymatic efficiency, besides catalytic Thr1 and Lys33 residues, the presence of aspartic acid in position 17 and an aqueous solvent is required, proving that the electrostatic potential generated by the remaining residues is insignificant for catalysis. Moreover, it was found that the gradual decay of atomic charges on Asp17 strongly correlates with the enzyme's catalytic rate deterioration as well as with a change in the charge distributions due to introduced mutations. The computational procedure used and described here may help identify key residues for catalysis in other biomolecular systems and consequently may contribute to the process of designing enzyme-like synthetic catalysts.

Flare-related plasma motions in the outer atmosphere of the RS CVn-type star II Peg

Analogous to solar flares, stellar flares are dramatic explosions in the atmosphere, which may be accompanied by prominence eruptions, coronal mass ejections (CMEs), and other forms of plasma motion. Based on time-resolved spectroscopic observations of the RS CVn-type star II Peg, we aim to search for the potential plasma motions associated with flares. In these observations, we detected part of the gradual decay phase of an optical flare, for which we find a lower limit on the energy of the H$ alpha $ line of $6.03 $ erg. Converting this H$ alpha $ energy, we find a bolometric white-light energy of $3.10 $ erg. Moreover, a secondary peak is also observed. After removing a quiescence reference, the H$ alpha $ residual shows an asymmetric behavior, including both a blueshifted and a redshifted emission component. The former component has a bulk velocity of about -180 km s$^ $ and extends its velocity to more than -350 km s$^ $. This phenomenon is likely caused by a prominence eruption event or a chromospheric evaporation process. The latter emission component has a bulk velocity of 130 to 70 km s$^ $ and extends its velocity to nearly 400 km s$^ $. We attribute the redshifted emission component to one or a combination of several possible scenarios: flare-driven coronal rain, chromospheric condensation, backward-directed prominence eruption close to the stellar limb, or falling material in a prominence eruption. The minimum masses of the moving plasmas resulting in the blueshifted and redshifted emission components are estimated to be $0.56 $ g and $1.74 $ g, respectively.

Interfacial deterioration in highly fluorinated cation-disordered rock-salt cathode: Carbonate-based electrolyte vs. ether-based electrolyte

Cation-disordered rock-salts (DRX) emerge as an intriguing class of high-capacity cathode materials, garnering significant attention in the development of advanced energy-storage systems. Fluorination strategies have been raised to regulate redox and structure for better DRX electrochemical performance. However, research on the interfacial processes during fluorinated DRX cycling remains limited. Here, we evaluate a highly fluorinated DRX, Li2Mn2/3Nb1/3O2F (LMNOF), in different electrolytes to correlate its cycling performance with distinct interfacial evolutions. During cycling in the carbonate-based electrolyte, a thick Mn-containing CEI forms on the LMNOF surface, leading to gradual capacity decay. Intriguingly, the addition of fluoroethylene carbonate (FEC) would bring about surface oxygen loss, Mn-ion dissolution and formation of a fluorinated surface layer by reacting with the LMNOF surface, which critically deteriorate the cycling performance. In comparison, the ether-based electrolyte is compatible with the LMNOF surface, resulting in a more favorable cycling stability. This work sheds light on the interfacial deterioration mechanism of LMNOF cathode in traditional carbonate-based electrolyte, emphasizing the importance of using advanced non-reactive electrolytes to enhance DRX performance.

Revealing the degradation pathways of layered Li-rich oxide cathodes.

Layered lithium-rich transition metal oxides are promising cathode candidates for high-energy-density lithium batteries due to the redox contributions from transition metal cations and oxygen anions. However, their practical application is hindered by gradual capacity fading and voltage decay. Although oxygen loss and phase transformation are recognized as primary factors, the structural deterioration, chemical rearrangement, kinetic and thermodynamic effects remain unclear. Here we integrate analysis of morphological, structural and oxidation state evolution from individual atoms to secondary particles. By performing nanoscale to microscale characterizations, distinct structural change pathways associated with intraparticle heterogeneous reactions are identified. The high level of oxygen defects formed throughout the particle by slow electrochemical activation triggers progressive phase transformation and the formation of nanovoids. Ultrafast lithium (de)intercalation leads to oxygen-distortion-dominated lattice displacement, transition metal ion dissolution and lithium site variation. These inhomogeneous and irreversible structural changes are responsible for the low initial Coulombic efficiency, and ongoing particle cracking and expansion in the subsequent cycles.

Co-seismic and post-seismic slip associated with the 2021 Mw5.9 Arkalochori, Central Crete (Greece) earthquake constrained by geodetic data and aftershocks

The co-seismic and post-seismic deformation field associated with the Mw5.9 Arkalochori main shock that occurred in central Crete (Greece) on 27 September 2021 is analyzed using Copernicus Sentinel-1A & 1B images, GNSS measurements and seismological data. The fault geometry is constrained through the joint inversion of multiple datasets and the slip distribution for the co-seismic and post-seismic period is obtained using a homogeneous half-space elastic model and the Steepest Descent Method. The results indicate a blind normal fault striking 215° with a 55° dip to the northwest and the co-seismic slip model suggests a nearly circular main slip patch (8 × 6 km2) with a maximum slip of 0.98 m. Post-seismic displacements started rapidly after the main shock followed by a gradual decay as highlighted by the calculated InSAR time series. The temporal evolution of post-seismic slip is described by a simple logarithmic function, decaying faster at the southwest part of the fault. The cumulative afterslip model suggests that the maximum post-seismic slip of 0.23 m occurred within a similar depth range compared to the co-seismic one, yet with a shift towards the southwest. Post-seismic slip inside the main shock rupture area is sustained, highlighting the slow recovery of locking in the co-seismic slip region. Afterslip (seismic or aseismic) played a dominant role in the early post-seismic period acting complementarily to the main rupture. Indications suggest that the spatiotemporal evolution of the productive aftershock sequence may be driven afterslip, alongside other potential factors.

Cyclo‐Bis(Acyl)phosphine Oxides as Efficient Photoinitiators for Radical Polymerization

AbstractAcyclic acylphosphine oxides have been extensively utilized in industrial applications as typical photoinitiators (PIs). In this study, we demonstrate the efficiency of their cyclic analogues, cyclo‐bis(acyl)phosphine oxides (CBAPOs), as efficient PIs. We present the isolation and X‐ray crystallographic characterization of CBAPOs. These compounds exhibit a long maximum absorption wavelength ranging between 415 and 420 nm, extending well into the near 500 nm region. Radical trapping experiments suggest that CBAPOs undergo homolytic P−C(O) bond α‐cleavage. Steady‐state photolysis conducted with LED light at 390 nm, monitored by UV‐Vis spectroscopy, confirms the gradual decay of CBAPOs over time. Additionally, all CBAPOs are capable of initiating radical polymerization under irradiation at 365 nm. Notably, one of the CBAPOs (4a) demonstrates comparable photoinitiating efficiency to one of commercially available bis(acyl)phosphine oxides (Irgacure 819).

Study on the effect of heating rate and temperature on the fracture properties of flawed granite

The effects of heating rate and temperature on fracture characteristics and mechanical properties of flawed granite were studied by using the cracked straight-through Brazilian disc specimen. Four temperature groups were established, and the specimens were heated in a furnace with different heating rates. After thermal treatment, the specimens were conducted to static compression tests, the compression process was recorded by a camera and the deformation on the specimen surface was calculated by the digital image correlation (DIC) technology. A microscope which can magnify nine times was employed to observe the surface of specimen and the transgranular or intergranular fracture. The results show that: at the same temperature, the thermal cracks increase as the heating rate increases. Within the same temperature group, the mode-I fracture toughness of granite shows a gradual decay characteristic as the rate of heating increases. Due to the DIC results, at the same temperature, when the heating rate increases, the maximum principal strain and the crack tip opening displacement (CTOD) of crack tip show an increasing trend at fracture. At 200 ℃, the maximum principal strain in the range of 0.0781% ∼ 0.237 %, the effect of heating rate is distinct. At 200–400 ℃, the input energy and release energy by fracture decrease with the heating rate. In the same temperature group, the specimen heating rate of 20 ℃/min has more distinct ductile characteristics.

Time-dependent Stellar Flare Models of Deep Atmospheric Heating

Optical flares have been observed from magnetically active stars for many decades; unsurprisingly, the spectra and temporal evolution are complicated. For example, the shortcomings of optically thin, static slab models have long been recognized when confronted with the observations. A less incorrect—but equally simple—phenomenological T ≈ 9000 K blackbody model has instead been widely adopted in the absence of realistic (i.e., observationally tested) time-dependent, atmospheric models that are readily available. We use the RADYN code to calculate a grid of 1D radiative-hydrodynamic stellar flare models that are driven by short pulses of electron-beam heating. The flare heating rates in the low atmosphere vary over many orders of magnitude in the grid, and we show that the models with high-energy electron beams compare well to the global trends in flux ratios from impulsive-phase stellar flare, optical spectra. The models also match detailed spectral line-shape properties. We find that the pressure broadening and optical depths account for the broad components of the hydrogen Balmer γ lines in a powerful flare with echelle spectra. The self-consistent formation of the wings and nearby continuum level provides insight into how high-energy electron-beam heating evolves from the impulsive to the gradual decay phase in white-light stellar flares. The grid is publicly available, and we discuss possible applications.

Experimental Co-Polarimetric GPR Survey on Artificial Vertical Concrete Cracks by the Improved Time-Varying Centroid Frequency Scheme

The experimental setup is devised to simulate the presence of vertical cracks with varying widths within concrete structures. Co-polarimetric ground-penetrating radar (GPR) surveys are carried out to acquire the “VV” and “HH” polarization data. The time-varying centroid frequency attribute is employed to describe the vertical variation in the center frequency of the radar wave, unveiling a gradual vertical decay in the centroid frequency at the locations of vertical cracks. An improved time-varying centroid frequency attribute based on the adaptive sparse S-transform (ASST) is proposed and tested by a finite-difference time-domain model and co-polarimetric GPR data, which can offer better resolution compared to that of the conventional S-transform. By analyzing the waveform and centroid frequency properties of the two polarizations, we conclude that the “VV” polarization is relatively sensitive to centimeter scale cracks, while the “HH” polarization is more sensitive to millimeter scale cracks.

Numerical modeling of inkjet cell output under the interplay of cell-laden bioink consumption and sedimentation

Inkjet printing utilizes the bioink involving biological materials and living cells to generate cell-laden droplets for precise construction of 3D tissue/organ models in a layer-by-layer manner. While printing, the suspended cells in bioink sediment due to predominant gravitational force, and form cell aggregates. It is increasingly difficult to transfer aggregates to the nozzle dispenser, resulting in gradual decay of the cell output, which becomes a critical challenge significantly affecting printing reliability and quality. This study has proposed a computational model coupling the cell flow field due to cell sedimentation and the bioink flow field due to bioink consumption. The modeled cell output has been validated by the experimental results showing a good agreement. Precise prediction of cell output enables optimization of the bioprinting process with less trial-and-error cost and promotes fabrication of more consistent and reproducible bioconstructs. The study finds that (1) the measured cell sedimentation velocity at bioink reservoir bottom increases due to the greater cell aggregates formed while printing; (2) the cell movement dynamics revealed by the model exhibit reduced movement from the sides towards the center of the bioink reservoir due to an increased sedimentation effect over printing; (3) the cell output decreases by 75 % within 60-minute printing at 400 Hz frequency. Applying greater inkjet frequency from 200 to 1000 Hz enables greater cell output efficiency from 0.48 to 0.93; (4) under 75 % preset efficiency criterion, applying frequency > 97 Hz for 60-minute printing is recommended to secure positive cell output considering the minimal threshold to counter sedimentation.

Indole-Based Compounds in the Development of Anti-Neurodegenerative Agents.

Neurodegeneration is a gradual decay process leading to the depletion of neurons in both the central and peripheral nervous systems, ultimately resulting in cognitive dysfunctions and the deterioration of brain functions, alongside a decline in motor skills and behavioral capabilities. Neurodegenerative disorders (NDs) impose a substantial socio-economic strain on society, aggravated by the advancing age of the world population and the absence of effective remedies, predicting a negative future. In this context, the urgency of discovering viable therapies is critical and, despite significant efforts by medicinal chemists in developing potential drug candidates and exploring various small molecules as therapeutics, regrettably, a truly effective treatment is yet to be found. Nitrogen heterocyclic compounds, and particularly those containing the indole nucleus, which has emerged as privileged scaffold, have attracted particular attention for a variety of pharmacological applications. This review analyzes the rational design strategy adopted by different research groups for the development of anti-neurodegenerative indole-based compounds which have the potential to modulate various molecular targets involved in NDs, with reference to the most recent advances between 2018 and 2023.

Accessibility and Equity Analysis of Highway-Railway Traffic Network Based on Real-Time Route Planning Data: A Case Study of Shandong Peninsula Urban Agglomeration, China

As a bond of geospatial and socioeconomic ties, transport supports the development of regions. With the rapid development of the economy, the coordinated development of regional transport has become a concern. To narrow the gap in transport development between cities and achieve sustainable development in regional transport, this study took the Shandong Peninsula urban agglomeration as the research object and using real-time path planning data assessed accessibility of the traffic network under two travel scenarios: cars and car-connected train. Based on the results of accessibility calculations, the Gini coefficient and Theil index were used to measure the equity of regional traffic networks. The results showed that (1) overall accessibility under the two travel scenarios showed a pattern of gradual decay from the center to the periphery; (2) both the accessibility and equity of the highway network were better than those of the railway network; (3) differences in regional development were the main sources of overall regional transport inequity. The research results provide a useful reference for the planning and construction of urban agglomeration traffic networks.

CFD simulations of helium layer erosion in one PANDA vessel following cooler activation

We performed CFD simulations of the two H2P6 cooler tests conducted in the PSI PANDA vessel as part of the OECD/NEA HYMERES-2 project. Initially, the vessel atmosphere consists of a 60/40 % vol. steam- air mixture. Then, a helium stratification (15 % vol.) is introduced in the upper half of the vessel. The two experiments H2P6_1 and H2P6_2 are characterized by the activation respectively of 3 and 1 cooler(s) in the upper part of the vessel. In the course of the experiments, condensation takes place, resulting in a gradual pressure decay and erosion of the helium layer until complete mixing is achieved.The URANS k-ε is used to model turbulence. CFD Best Practice Guidelines are followed to minimize numerical errors, with preliminary mesh sensitivity studies. A correlation based on the heat-and-mass transfer analogy is employed to estimate steam condensation rates.Each cooler consisting of 18 tubes is simplified into a cuboid with equivalent heat transfer area. In a further simplification, it is assumed that the cooler wall has a thickness of zero and is initially at the temperature of the coolant. The small initial energy stored in the mass of the cooler at time zero is therefore neglected.The simulation for H2P6_1 matches the main experimental parameters (heat removal rate, pressure, species concentrations) almost perfectly. For H2P6_2 the heat removal rate is slightly under-predicted, with a corresponding over-prediction of the pressure by a maximum of 3 %. The inclusion of radiative heat transfer modeling improves the accuracy of the temperature field but has little influence on the pressure or heat removal histories.These results show that CFD allows accurate predictions of containment mixing when coolers are activated. Moreover, the simulations also indicate that multiple cooler units can be represented by one larger equivalent unit.

Charge transport and ion migration in perovskite-incorporated conjugated polymer semiconductor

The migration of intrinsic ions in metal halide perovskites and their interfaces has been shown to contribute to hysteresis and performance degradation in perovskite-based electronic devices, particularly in photovoltaics and transistors. Accordingly, controlling the film morphology, microstructure, and ionic defects in perovskite semiconductors is essential for advancing and achieving high-performance perovskite field-effect transistors (FETs). In this study, we demonstrate a well-controlled method to systematically probe the structure-property relationships, origin of hysteresis, and intrinsic ion migration effects in formamidinium iodide and lead iodide (FAI + PbI2)-based perovskite by incorporating it in a semicrystalline conjugated poly(3-hexylthiophene) (P3HT) polymer. Optimized FETs exhibited over 100% hole mobility enhancement owing to unperturbed edge-on crystalline orientation of the P3HT chains caused by the incorporated perovskite, P3HT-(FAI + PbI2) interactions, and better charge injection properties. However, the optimized devices exhibited improved current modulation with dual-sweep hysteresis, which was attributed to the ion migration effect contributed by the polarization of the lead/iodine-related ions and defects. Furthermore, operational stability investigation of the P3HT-(FAI + PbI2) FETs in the air revealed gradual current decay owing to charge trapping in contrast to the control P3HT FETs. This work provides a fundamental understanding of the origin of hysteresis and instabilities in metal perovskite materials and their transistor-based devices.

Decay rate of the solutions to the Cauchy problem of the Lord Shulman thermoelastic Timoshenko model with distributed delay

Abstract In this study, we address a Cauchy problem within the context of the one-dimensional Timoshenko system, incorporating a distributed delay term. The heat conduction aspect is described by the Lord-Shulman theory. Our demonstration establishes that the dissipation resulting from the coupling of the Timoshenko system with Lord-Shulman’s heat conduction is sufficiently robust to stabilize the system, albeit with a gradual decay rate. To support our findings, we convert the system into a first-order form and, utilizing the energy method in Fourier space, and derive point wise estimates for the Fourier transform of the solution. These estimates, in turn, provide evidence for the slow decay of the solution.

Absorption-Based Rapid Acquisition of Single-Molecule Kinetics from Unstable Enzymes in Microdroplets.

Single-molecule catalysis reflects the heterogeneity of each molecule, providing a unique insight into the complex catalytic mechanism through the statistics of stochastic individuals. However, the present study methods for single-molecule catalysis are either complicated or have low throughput, limiting their rapid acquisition of single-molecule reaction kinetics with statistical significance. Here, a label-free imaging method is developed for the study of single-molecule catalysis in microdroplets with high throughput based on the absorption of the reaction molecules. A wide distribution of the catalytic reaction rate constant value of 238-2026 moleculess-1 is observed from 68 single enzymes. Interestingly, an exponential decayed distribution of the enzyme activity can be clearly observed due to the rapid denaturation of the enzymes. The denaturation mechanism of the Horse Radish Peroxidase (HRP)enzyme is clarified. It is revealed that the denaturation of each enzyme goes through a gradual decay rather than a truncated turn-off process from a single molecule point of view. This absorption-based method can be applied to most of the catalytic reactions with high throughput, which offers an indispensable route for the rapid statistical analysis of various single-molecule catalytic reactions, making it particularly suitable for the acquisition of catalytic kinetics from highly unstable enzymes.

Early Bruise Detection in Apple Based on an Improved Faster RCNN Model

Bruising is a common occurrence in apples that can lead to gradual fruit decay and substantial economic losses. Due to the lack of visible external features, the detection of early-stage bruising (occurring within 0.5 h) is difficult. Moreover, the identification of stems and calyxes is also important. Here, we studied the use of the short-wave infrared (SWIR) camera and the Faster RCNN model to enable the identification of bruises on apples. To evaluate the effectiveness of early bruise detection by SWIR bands compared to the visible/near-infrared (Vis/NIR) bands, a hybrid dataset with images from two cameras with different bands was used for validation. To improve the accuracy of the model in detecting apple bruises, calyxes, and stems, several improvements are implemented. Firstly, the Feature Pyramid Network (FPN) structure was integrated into the ResNet50 feature extraction network. Additionally, the Normalization-based Attention Module (NAM) was incorporated into the residual network, serving to bolster the attention of model towards detection targets while effectively mitigating the impact of irrelevant features. To reduce false positives and negatives, the Intersection over Union (IoU) metric was replaced with the Complete-IoU (CIoU). Comparison of the detection performance of the Faster RCNN model, YOLOv4P model, YOLOv5s model, and the improved Faster RCNN model, showed that the improved model had the best evaluation indicators. It achieved a mean Average Precision (mAP) of 97.4% and F1 score of 0.87. The results of research indicate that it is possible to accurately and effectively identify early bruises, calyxes, and stems on apples using SWIR cameras and deep learning models. This provides new ideas for real-time online sorting of apples for the presence of bruises.