Abstract We report the detection of a long X-ray burst from the ultracompact binary 4U 1850–087. The type I X-ray burst was observed on MJD 60171.65 by the Monitor of All-sky X-ray Image and Neutron ...Star Interior Composition Explorer (NICER). We analyze the NICER data between MJD 60095.19 and 60177.43, which includes the observation covering parts of the long X-ray burst decay phase, i.e., 0.15–3.8 hr after the trigger. The persistent spectra are well described by a multicolor disk blackbody, with an inner temperature of ∼0.5 keV, a thermally Comptonized continuum, an asymptotic power-law photon index of Γ ∼ 2.2, and an electron temperature of kT e ∼ 20–30 keV. The mean persistent flux was around 3.8 × 10 −10 erg cm −2 s −1 , corresponding to a local mass accretion rate of ∼ 1 % m ̇ Edd . Part of the time-resolved burst spectra show a clear deviation from the blackbody model, which can be improved by considering the enhanced persistent emission due to the Poynting–Robertson drag or the reflected disk emission illuminated by the burst. From the burst flux during the cooling phase, we estimate the burst duration, τ ≈ 0.78 hr, the burst fluence, E b ≈ 4.1 × 10 41 erg, and the ignition column depth, y ign ≈ 3.5 × 10 10 g cm −2 . These long X-ray burst parameters from 4U 1850–087 suggest a regime of unstable burning of a thick, pure helium layer slowly accreted from a helium donor star. Moreover, we identify 7 σ significant ∼1 keV emission lines in the burst spectra, which may originate from the surrounding accretion disk.
A novel potassium-carbonate-based absorption process is currently being developed to reduce the energy consumption when capturing CO2 from coal combustion flue gas. The process employs the enzyme ...carbonic anhydrase (CA) as a catalyst to accelerate the rate of CO2 absorption. This study focused on the immobilization of a new variant of the CA enzyme onto a new group of nonporous nanoparticles to improve the enzyme’s thermal stability and its chemical resistance to major impurities from the flue gas. The CA enzyme was manufactured at the pilot scale by a leading enzyme company. As carrier materials, two different batches of SiO2–ZrO2 composite nanoparticles and one batch of silica nanoparticle were synthesized using a flame spray pyrolysis method. Classic Danckwerts absorption theory with reaction was applied to determine the kinetics of the immobilized enzymes for CO2 absorption. The immobilized enzymes retained 56–88% of their original activity in a K2CO3/KHCO3 solution over a 60-day test period at 50 °C, compared with a 30% activity retention for their free CA enzyme counterpart. The immobilized CA enzymes also revealed improved chemical stability. The inactivation kinetics of the free and immobilized CA enzymes in the K2CO3/KHCO3 solution were experimentally quantified.
In the task of fusing infrared and visible images, the extraction of features and fusion strategy significantly impacts the outcome of the fusion. However, prevailing fusion methods are often ...manually designed, unlearnable, and neglect to consider context adequately. To address these issues, this paper introduces a distributed architecture network based on attention mechanism and dense dilated convolution, realizing three-channel data fusion. This network employs a distributed fusion framework to fully utilize the fusion output of the previous step, capitalizing effectively on the target and texture information in infrared and visible images. Initially, two channels gather ample context from the source images through a dense dilated convolution module with multiscale channel attention. Subsequently, a fusion strategy based on coordinate mean attention is adopted to facilitate the fusion of results between the two channels. Then, the fused features and the preceding fusion results are fed into the fusion channel, minimizing loss of target and texture information in infrared and visible images. Furthermore, we incorporate an edge correction block, capable of refining the edge details of the fusion results and effectively suppressing noise. The proposed method demonstrates good fusion performance and extensive ablation experiments validate the effectiveness of the proposed methodology. Simultaneously, both subjective qualitative and objective quantitative comparison results, conducted on public datasets such as RoadScene, TNO, and MSRS, indicate that the visual quality and evaluation metrics of our fusion images are comparable to those achieved by the state-of-the-art image fusion methods.
Reactive dynamics simulations with the reactive force field (ReaxFF) were performed in NVE ensembles to study the sintering of two solid calcium oxide (CaO) particles with and without CO(2) ...chemisorption. The simulated sintering conditions included starting adsorption temperatures at 1000 K and 1500 K and particle separation distances of 0.3 and 0.5 nm. The results revealed that the expansion of sorbent particles during CO(2) chemisorption was attributed to the sintering of two CaO-CaO particles. Increasing the adsorption temperature resulted in more particle expansion and sintering. The shorter the distance between two particles, the faster the rate of sintering during CO(2) adsorption. A detailed analysis on atom spatial variations revealed that the sorbent particles with a larger separation distance had a larger CO(2) uptake because of less sintering incurred. The chemisorptions of CO(2) on CaO particles sintered at high adsorption temperatures were also simulated to mimic the process of sorbent regeneration. It was found that regeneration would be more difficult for sintered particles than for fresh particles. In addition, a possible sintering barrier, magnesium oxide (MgO), was introduced to prevent CaO particles from sintering during CO(2) chemisorption. It was found that the MgO particles could reduce the sintering of CaO particles during CO(2) chemisorption. Simulation results from this study provided some guidelines on synthesizing or selecting sorbents with less sintering effect for multiple CO(2) adsorption-regeneration cycles.
A sorption-enhanced water–gas-shift reaction process (SEWGS) combines the WGS reaction and CO2 removal into a single process step in an integrated gasification combined cycle (IGCC) power plant. In ...the SEWGS, a solid sorbent is employed to capture the CO2 generated by the WGS reaction. A key technical issue for the SEWGS is to identify and develop sorbents that can capture CO2 under high pressure and high temperature syngas conditions and minimize or even eliminate the need for WGS catalysts. We present the results from a thermodynamic analysis and process simulation study that aimed to identify sorbents and optimal temperature windows to maximize the thermal efficiency of an IGCC + SEWGS plant. The results from the thermodynamic analysis identified two metal oxides, one silicate, three zirconates, and one titanate sorbents that are suitable for the SEWGS application. The results from the process simulation study revealed that the overall thermal efficiency of a 1187 MWth (thermal input) IGCC + SEWGS plant gasifying an Illinois coal, and using the seven sorbents selected from the thermodynamic analysis, was between 0.5 and 2.4 percentage points greater than that of a reference IGCC + Selexol plant.
•Thermodynamic criteria were developed to screen SEWGS sorbents.•Seven sorbents were identified thermodynamically suitable for SEWGS application.•Process simulation revealed superior energy efficiency of an IGCC + SEWGS plant.
Carbonic anhydrase (CA) enzyme-mediated absorption processes are regarded as promising alternatives to the conventional amine-based process for CO2 capture because of their low energy penalty and low ...risk of causing secondary pollution. The activity and stability of the CA enzyme are crucial to reducing the equipment and operating costs of the enzyme-mediated process. This work investigated three cationic and nonionic surfactants to improve the activity and stability of a technical-grade CA enzyme in a 20 wt % potassium carbonate solution. Experimental results revealed that the impact of the surfactants on the CA enzyme depended on their properties. For example, the cationic surfactant significantly enhanced the activity of CA enzyme but adversely affected enzyme stability. However, in the presence of the cationic surfactant after 30 days at 50 °C, the activity of the CA enzyme still outperformed that of CA without added surfactant. The nonionic surfactant significantly improved enzyme stability. Furthermore, the addition of surfactants within a critical micelle concentration of 1.0 did not distinctly influence the gas–liquid mass transfer, indicating that surfactant–enzyme interaction was responsible for the observed variations in the activity and stability of the tested enzyme.
Abstract
Type-I X-ray burst oscillations are powered by thermonuclear energy released on the neutron star (NS) surface in low-mass X-ray binaries (LMXBs), where the burst oscillation frequencies are ...close to the NS spin rates. In this work, we report the detection of oscillation at 584.65 Hz during the cooling tail of type-I X-ray bursts observed from the accreting NS LMXB 4U 1730–22 on 2022 March 20, by the Neutron star Interior Composition Explorer telescope. The oscillation signal showed a strong Leahy power,
P
m
∼ 54.04, around 584.65 Hz, which has single-trial and multiple-trial confidence levels of 7.05
σ
and 4.73
σ
, respectively. The folded pulse profile of the oscillation in the 0.2–10 keV band showed a sinusoidal shape with the fractional rms amplitude of (8.0 ± 1.1)%. We found the oscillation frequency showed insignificant upward drifting, i.e., less than 0.3 Hz, during the cooling tail, similar to the behavior appearing in accreting millisecond X-ray pulsars (AMXP), and indicate the source could be an AMXP spinning at 1.71 ms.
•The CA enzyme activity did not change noticeably with CO2 loading in a PC solution.•Absorption rate into CO2-rich PC with 3g/L of CA were twice that into a rich 5M MEA.•Liquid-phase mass transfer ...resistance dominated in both the PC and MEA systems.•Packing volume of IVCAP absorber with 10g/L of CA was comparable with that of MEA.
Development of enzyme-mediated solvents are regarded as a potential option to overcome the energy use disadvantages associated with the benchmark monoethanolamine (MEA) solvent for post-combustion CO2 capture. In this work, the kinetics of CO2 absorption into a 20wt% potassium carbonate (PC) solution promoted with the enzyme carbonic anhydrase (CA) was investigated using a stirred tank reactor. Experimental results showed no noticeable change in the intrinsic activity of the CA enzyme with increasing CO2 loading in PC solution. A rate-based mass transfer analysis was conducted using the enzymatic kinetics measured, and results revealed that in a packed-bed column, the CO2 absorption rates into a lean and rich PC solution with 3gL−1 CA were 50% lower and 2.2 times higher, respectively, than those into their 5M MEA counterparts. The liquid-phase mass transfer resistance was dominant for both PC- and MEA-based systems. Modeling results revealed the effective packing volume of the absorber with PC in the presence of 10gL−1 CA was only slightly larger than that with MEA for post-combustion CO2 capture.
•Both liquid–solid and liquid–liquid phase change solvents critically reviewed.•Various mechanisms triggering phase separations in solvents elucidated in detail.•Advantages and challenges of phase ...change processes for CO2 capture assessed.•Gaps between state-of-the-art and ideal solvents analyzed.•Insights into research needs regarding solvents and desired properties provided.
Carbon Capture and Storage is regarded as an important component in a portfolio of low-carbon energy technologies for mitigating climate change. Absorption technologies are presently the most available and effective approach for post-combustion CO2 capture. However, state-of-the-art amine-based absorption technologies incur intensive energy use, as high as 3 times the thermodynamic minimum, thus resulting in prohibitively high costs. Solvents are key to the performance of absorption technologies. Recently, a new class of solvents, phase change solvents, have attracted growing interest due to their potential to substantially reduce energy use for CO2 capture. Phase change solvents are homogeneous (single-phase) solvents under normal conditions, but undergo a phase transition into a heterogenic (two-phase) system, triggered by changes in polarity, hydrophilicity, ionic strength, or hydrogen bond strength to form a CO2-lean liquid phase and a CO2-enriched liquid or solid phase. This review paper first examines different mechanisms that trigger phase separations in solvents. A comprehensive list of phase change solvents reported in the recent literature, including those subject to chemically or thermally triggered phase changes, non-aqueous or aqueous systems, and those forming either a CO2-enriched solid or a liquid phase are provided and their physiochemical properties for CO2 capture are discussed. Enabled by phase change solvents, different variants of CO2 absorption processes have been developed and tested in laboratory or pilot scales over the past ten years. The status of such emerging processes is summarized and their advantages and challenges for post-combustion CO2 capture are reviewed and commented. Solvent properties such as CO2 loading capacity, lean- and rich-phase partition, desorption pressure, absorption kinetics, viscosity, stability, and volatility are critical for both CO2 capture performance and scalability. Gaps between state-of-the-art and ideal solvents are analyzed, and insights into the research needs such as solvent structure–property–performance relations, computational solvent design, ideal vapor-liquid equilibrium behavior, and integration of capture processes with post-combustion emission sources are provided.
Aquaporin-8 (AQP8), a member of the aquaporin family, is strongly expressed in follicular granulosa cells, which could affect the hormone secretion level in females. AQP8, as a membrane protein, ...could mediate H
2
O
2
into cells, thereby triggering various biological events. The deficiency of
Aqp8
increases female fertility, resulting from the decrease in follicular atresia. The low cell death rate is related to the apoptosis of granulosa cells. However, the mechanism by which AQP8 regulates the autophagy of granulosa cells remains unclear. Thus, this study aimed to explore the effect of AQP8 on autophagy in follicular atresia. We found that the expression of the autophagy marker light-chain protein 3 was significantly downregulated in the granulosa cells of
Aqp8
-knockout (
Aqp8
−/−
) mice, compared with wild-type (
Aqp8
+/+
) mice. Immunofluorescence staining and transmission electron microscopic examination indicated that the number of autophagosomes in the granulosa cells of
Aqp8
−/−
mice decreased. Using a follicular granulosa cell autophagy model, namely a follicular atresia model, we verified that the concentration of H
2
O
2
significantly increased during the autophagy of granulosa cells, consistent with the
Aqp8
mRNA level. Intracellular H
2
O
2
accumulation was modulated by endogenous AQP8 expression level, indicating that AQP8-mediated H
2
O
2
was involved in the autophagy of granulosa cells. AQP8 deficiency impaired the elevation of H
2
O
2
concentration through phosphorylated tyrosine activation. In addition, we carried out the analysis of transcriptome sequencing datasets in the ovary and found there were obvious differences in principal components, differentially expressed genes (DEGs) and KEGG pathways, which might be involved in AQP8-regulated follicular atresia. Taken together, these findings indicated that AQP8-mediated H
2
O
2
transport could mediate the autophagy of granulosa cells. AQP8 might be a potential target for diseases related to ovarian insufficiency.
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