LB-1 is a binary system that has drawn great attention since its discovery in 2019.The two components of LB-1 are suggested to be a B-type star plus a black hole (BH).In this paper,we first calculate the wind mass-los...LB-1 is a binary system that has drawn great attention since its discovery in 2019.The two components of LB-1 are suggested to be a B-type star plus a black hole (BH).In this paper,we first calculate the wind mass-loss rate of the B-type star.We then calculate the mass capture rate by the BH,with which as the initial mass accretion rate,we calculate the truncation radius of the accretion disk and the corresponding emergent spectra of the accretion flow(comprising an inner advection-dominated accretion flow (ADAF)+an outer truncated accretion disk) within the framework of the disk evaporation model.It is found that the predicted truncation radius of the accretion disk with appropriate model parameters is consistent with observations inferred from the observed broad H_(α) emission line.The predicted X-ray luminosity is definitely below the estimated upper limits with the sensitivity of the Chandra X-ray Observatory of the X-ray luminosity≈2×10^(31)ergs^(-1),which is also consistent with observations.Finally,we argue that the disk evaporation model can indeed reflect the intrinsic physics of the accretion flow in LB-1,and has potential to be applied to other quiescent BHs in the future.展开更多
Changes in the coastline are characterized by accretion and erosion. The aim of this study is to contribute to a better understanding of the dynamics of the coastline and the study areas with a view to mitigating and ...Changes in the coastline are characterized by accretion and erosion. The aim of this study is to contribute to a better understanding of the dynamics of the coastline and the study areas with a view to mitigating and preventing the risk of coastal erosion in order to propose a coastal occupation model with planned development policies in the future. These phenomena lead to changes in the position of the coastline. After extraction, the satellite images are compiled, then superimposed and processed using Geographic Information Systems (GIS) for statistical calculation of coastline change rates. A morphosedimentary study is carried out using topography and sedimentology. The topographic method is used to calculate sediment volumes using monthly profiles. The sedimentological method is used to determine the granulometric variations in the morphological units by calculating sedimentological indices. With erosion rates of −2.13 m/yr and −2.17 m/yr respectively at Djiffère (Palmarin and Sangomar breccia) and Joal (Joal Fadhiouth and Ngazobil), the EPR index revealed a sediment deficit. Palmarin Ngallou and the island of Fadhiouth are undergoing accretion at rates of +1.43 m/yr and +1.14 m/yr respectively. From a topographical point of view, the respective accumulations of −13.74 m3/m of beach and −8.65 m3/m of beach at Djiffère and Joal respectively point to significant erosion on all the aerial beach units, while for the underwater beaches, accretion was noted with accumulations of +4.00 m3/m of beach and +5.94 m3/m at Djiffère and Joal respectively. As for the sedimentological results, the Mz index shows a decrease in grain size from the high beach to the surf zone. Some points show bimodal deposits, showing the impact of the dune on beach activity, confirmed by the dispersion on the Mz-sigma diagram. The three methods used in this work show that the Djiffère sector in Joal is dominated by erosion, even though accretion points can be noted.展开更多
This paper investigates the star formation efficiency(SFE)of blue compact galaxies(BCGs)by analyzing various indicators,including(O II),(H_(α)),infrared emissions,and the 1.4 GHz radio continuum.The assessment of SFE...This paper investigates the star formation efficiency(SFE)of blue compact galaxies(BCGs)by analyzing various indicators,including(O II),(H_(α)),infrared emissions,and the 1.4 GHz radio continuum.The assessment of SFE was conducted using publicly accessible data that concentrated on star formation rates(SFRs)and depletion timescales.By employing the fundamental equation,I determined the SFE in relation to its freefall time,which highlighted variations in efficiencies associated with SFR masses derived from different spectra.The results demonstrated that the highest efficiency value was observed in the analysis of the 1.4 GHz radio continuum,emphasizing the importance of studying star-forming clouds across a range of electromagnetic wavelengths to achieve a comprehensive understanding of star formation mechanisms.The study's findings indicated a peak efficiency of star formation value of approximately 0.9%,while the relative minimum obtained from(O II)was around 0.42%,aligning with the range of SFEs documented in the existing literature.Additionally,investigating the factors that influence the variability in efficiency when examining clouds in BCGs across different wave bands is crucial for deepening our comprehension of the underlying processes of star formation.展开更多
We conducted an analysis of the continuum during the onset and initial decline phases of the 2023 outburst in transient neutron star low-mass X-ray binary Aql X–1 using broadband observations from the Hard X-ray Modu...We conducted an analysis of the continuum during the onset and initial decline phases of the 2023 outburst in transient neutron star low-mass X-ray binary Aql X–1 using broadband observations from the Hard X-ray Modulation Telescope(Insight-HXMT)instrument.To determine the most appropriate model for the continuum of this outburst,we employed three models to explore the evolution of the spectral component.These observations revealed that the source transitions from the hard state to the soft state.The disk-corona and sphere-corona models both adequately described the spectra of the hard state,while the double blackbody model became preferable after the hard X-ray emission(>25 keV)disappeared during the state transition.In the soft state,the total emission is dominated by the accretion disk and two blackbody components.The combination of the sphere-corona model and the double blackbody model is the most suitable model for this outburst.The results suggest that as the source transitioned into the soft state,the emission from the boundary layer was enhanced,and a hot spot occurred.Notably,we identified two type-ⅠX-ray bursts,one of which exhibited a significant hard X-ray deficit(significance~4.82σ),which indicates that Insight-HXMT has the capability to capture the evolution of the corona in a single burst.展开更多
Changing-look(CL)active galactic nuclei(AGNs)are an extremely rare type of AGNs,characterized by the appearance(turn-on)or disappearance(turn-off)of broad emission lines within months to years.We construct a sample of...Changing-look(CL)active galactic nuclei(AGNs)are an extremely rare type of AGNs,characterized by the appearance(turn-on)or disappearance(turn-off)of broad emission lines within months to years.We construct a sample of 211 CL AGN candidates by systematically searching the Sloan Digital Sky Survey spectra classified as GALAXY,but with the Zwicky Transient Facility and Near-Earth Object Wide-Field Infrared Explorer midinfrared light curves showing significant variability,at the redshift range from 0.1 to 0.75.To examine the success rate of this method,we cross-match the candidate sample with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope and the Dark Energy Spectroscopic Instrument for repeat spectra,finding that the success rate of this method is 50%.By incorporating previously reported CL AGNs,a total of 48 CL AGNs have been identified within our sample,including two recurrent CL AGNs newly confirmed in this work.Our results suggest that the typical rest-frame timescale of CL behavior is from 1.7 to 18.1 yr,which is inconsistent with the obscuration model,and the Eddington ratios of CL AGNs are about 0.01 in the bright state.Additionally,our CL AGN sample follows the M_(BH)–σ_(*)relation of quiescent galaxies.In the future,we expect to detect more galaxies turning into Type 1 AGNs in this CL AGN candidate sample.展开更多
We present simulation results examining the presence and behavior of standing shocks in zero-energy low angular momentum advective accretion flows and explore their(in)stability properties,taking into account various ...We present simulation results examining the presence and behavior of standing shocks in zero-energy low angular momentum advective accretion flows and explore their(in)stability properties,taking into account various values of specific angular momentum,λ_(0).Within the range 10-50R_(g)(where R_(g)denotes the Schwarzschild radius),shocks are discernible forλ_(0)≥1.75.In the special relativistic hydrodynamic simulation whenλ_(0)=1.80,we find the merger of two shocks resulted in a dramatic increase in luminosity.We present the impact of external and internal flow collisions from the funnel region on luminosity.Notably,oscillatory behavior characterizes shocks within 1.70≤λ_(0)≤1.80.Using free–free emission as a proxy for analysis,we show that the luminosity oscillations between frequencies of 0.1-10 Hz forλ_(0)range as 1.7≤λ_(0)≤1.80.These findings offer insights into quasiperiodic oscillation emissions from certain black hole X-ray binaries,exemplified by GX 339-4.Furthermore,for the supermassive black hole at the Milky Way's center,Sgr A*,oscillation frequencies between 10^(-6)and 10^(-5)Hz were observed.This frequency range,translating to one cycle every few days,aligns with observational data from X-ray telescopes such as Chandra,Swift,and XMM-Newton.展开更多
We present the results of a multi-epoch,detailed spectral and temporal analysis of the ultraluminous X-ray source(ULX),ULX-1,in the galaxy NGC 4088 using XMM-Newton,Chandra,and Swift observations.The presence of a har...We present the results of a multi-epoch,detailed spectral and temporal analysis of the ultraluminous X-ray source(ULX),ULX-1,in the galaxy NGC 4088 using XMM-Newton,Chandra,and Swift observations.The presence of a hard powerlaw spectral slope supports the interpretation of ULX-1 as a hard ULX.The observed inner disk temperature of kT_(in)> 1.5 keV is inconsistent with the presence of an intermediate mass black hole,but favors the super-Eddington accretion state.Moreover,the physically acceptable value of the parameter controlling the radial temperature profile of the disk(p) derived from fitting the first XMM-Newton observation with the slim disk model further points towards the possible presence of a broadened disk,indicating the super-Eddington accretion nature.Slight overall long-term flux variability is evident for this ULX,and a hint towards a positive correlation between flux and the powerlaw photon index is also observed when the relatively better data of XMM-Newton and Chandra are considered.The L-T relationship is observed to follow a positive trend,with the L-T profile consistent with either relation(L ∝ T^(4) or L ∝ T^(2)) in both cases.The source exhibits no significant short-term variability at different time binnings of the light curve as indicated by the chi-square probability of constancy and fractional RMS variability values.The power density spectrum created shows no evidence of intrinsic variability of the source above the white noise.Further,no sign of pulsation was detected for this source.Assuming this ULX to be powered by an accreting black hole and using the slim disk geometry,the upper limit of the black hole mass was estimated and found to be less than 100M_(⊙).展开更多
The ice accretion on the wing surface of aircraft significantly impacts flight safety.Providing a precise safety assessment by examining flight characteristics and meteorological conditions is challenging.Based on dif...The ice accretion on the wing surface of aircraft significantly impacts flight safety.Providing a precise safety assessment by examining flight characteristics and meteorological conditions is challenging.Based on different swept angles,the experimental data from the icing wind tunnel establish the geometric link between the position of the wingspan and the shape of ice accretion at the leading edge.The correlation analysis and Sobol sensitivity are used to study the uncertainty of single variable.Simultaneously,the polynomial chaos method is employed to study the uncertainty of multiple variables.The results indicate significant correlation between the angle of attack and lift and drag coefficients.The influence of height and velocity on sensitivity is negligible,with the aerodynamic characteristics mostly dependent on the geometric attributes of the ice structure.The uncertainty propagation framework established can accurately assess the impact of swept angle on the aerodynamic parameters of the icing wing,and the predicted findings fall within a 95%confidence interval.展开更多
This study explores the dynamics of charged Hayward black holes,focusing on the effects of electric charge and the length factor on accretion disk characteristics.Our results show that increasing both parameters reduc...This study explores the dynamics of charged Hayward black holes,focusing on the effects of electric charge and the length factor on accretion disk characteristics.Our results show that increasing both parameters reduces the size of the event horizon and innermost stable circular orbits(ISCO)radius,with the electric charge exerting a more pronounced influence.Additionally,the length factor and electric charge can effectively replicate the spin of a Kerr black hole.Both parameters also affect the electromagnetic radiation emitted from the accretion disk,increasing the flux,temperature,and radiative efficiency.The peak radiation occurs in the soft x-ray band,with higher values of electric charge and length factor enhancing disk luminosity and shifting the peak to higher frequencies.These findings can offer valuable insights into the accretion processes around black holes and their observable signatures,particularly in x-ray astronomy.展开更多
Polar ships face significant risks from ice accretion on decks,superstructures,and power systems.Ice formation on the power intake system particularly affects vessel stability and safety.While freshwater icing has bee...Polar ships face significant risks from ice accretion on decks,superstructures,and power systems.Ice formation on the power intake system particularly affects vessel stability and safety.While freshwater icing has been extensively researched,comprehensive multi-parameter studies on ice accretion for intake structures remain insufficient.This investigation examines the icing characteristics of the air shroud,a critical component of marine gas turbines,resulting from saltwater droplet freezing.The study utilized a custom-built cyclic ice wind tunnel,with flow field quality verified through Five-hole probe and Hot wire anemometer methods,and droplet field quality validated using Laser,Flowmeter,Ice blade,and Icing calibration grid techniques.The research analyzes ice distribution and thickness on the shroud under varying NaCl concentrations,considering temperature,liquid water content(LWC),and median volume diameter(MVD).The findings reveal that decreased salinity facilitates rime ice formation,resulting in rough ice texture.Temperature reduction,increased LWC,and larger MVD enhanced salinity's influence on ice thickness.The shroud exhibits substantial radial ice accretion,with coverage extending to approximately 90%.These results establish a foundation for further investigation of saltwater icing mechanisms and pioneer icing research in marine gas turbine intake systems.展开更多
The mechanism of continental crust growth remains ambiguous.A key constraint is determining which tectonic settings were involved in the formation of the new continental crust.Because the basalts formed in intraplate(...The mechanism of continental crust growth remains ambiguous.A key constraint is determining which tectonic settings were involved in the formation of the new continental crust.Because the basalts formed in intraplate(OIB,mean U/Pb=~0.37±0.11)and subduction(IAB,mean U/Pb=~0.10±0.06)settings have distinct U/Pb ratios,thus we back-calculate the present-day U/Pb ratios of the New Continental crust source[(U/Pb)_(nc)]based on our zircon-Hf and published whole rock-Pb isotope compositions of the WulagaⅠ-type granite to unfold the mechanism of the crust growth in the Lesser Xing'an Range(LXR),of the eastern Central Asian orogenic belt(CAOB).The Wulaga granodiorite porphyry yields zircon U-Pb ages of 103±1 Ma withε_(Hf)(t)of+6.0 to+9.0 and T_(DM2)of 590 to 784 Ma(averaging at 709±100 Ma).This result indicates that the Early Cretaceous Wulaga granodiorite porphyry was derived from the Neoproterozoic juvenile basaltic crust.The back-calculated(U/Pb)_(nc)values(0.15-0.18)may approximately represent the U/Pb ratios of the basaltic protolith of the Wulaga granite.It is similar to the U/Pb ratios in the IAB magmas within the calculation errors.Therefore,the crust growth of the LXR may occur through subduction at ca.700 Ma.In addition,this geochemical method also has been successfully applied to unfold the mechanism of the crust accretion of both the Jibei area in North China at ca.2.0 Ga and the Hongol area in the eastern CAOB during ca.1.1-0.8 Ga.The back-calculation of the present U/Pb ratio of the protolith ofⅠ-type granites in this study may constitute a potential method to constrain the mechanism of continental crustal accretion.展开更多
This study presents a data-driven approach to predict tailplane aerodynamics in icing conditions,supporting the ice-tolerant design of aircraft horizontal stabilizers.The core of this work is a low-cost predictive mod...This study presents a data-driven approach to predict tailplane aerodynamics in icing conditions,supporting the ice-tolerant design of aircraft horizontal stabilizers.The core of this work is a low-cost predictive model for analyzing icing effects on swept tailplanes.The method relies on a multi-fidelity data gathering campaign,enabling seamless integration into multidisciplinary aircraft design workflows.A dataset of iced airfoil shapes was generated using 2D inviscid methods across various flight conditions.High-fidelity CFD simulations were conducted on both clean and iced geometries,forming a multidimensional aerodynamic database.This 2D database feeds a nonlinear vortex lattice method to estimate 3D aerodynamic characteristics,following a'quasi-3D'approach.The resulting reduced-order model delivers fast aerodynamic performance estimates of iced tailplanes.To demonstrate its effectiveness,optimal ice-tolerant tailplane designs were selected from a range of feasible shapes based on a reference transport aircraft.The analysis validates the model's reliability,accuracy,and limitations concerning 3D ice shapes and aerodynamic characteristics.Most notably,the model offers near-zero computational cost compared to high-fidelity simulations,making it a valuable tool for efficient aircraft design.展开更多
Most massive stars reside in binary or multi-object systems.Short gamma-ray bursts(sGRBs),the product of the merger of double compact objects,may originate from massive common-envelope binaries.In contrast,the progeni...Most massive stars reside in binary or multi-object systems.Short gamma-ray bursts(sGRBs),the product of the merger of double compact objects,may originate from massive common-envelope binaries.In contrast,the progenitors of long GRBs(lGRBs)are typically considered isolated massive stars.However,no effective method has yet been established to identify potential companions from current observations.Recent studies have demonstrated that quasi-periodic oscillation signatures can serve as a promising tool to probe the properties of GRB central engines.In this study,by drawing an analogy to periodicity in X-ray binaries,we explore the precession periods of companion-induced disk precession for lGRBs born in the ultra-compact binary scenario.Our results suggest that the periodicity observed in lGRB afterglows,measured in units of 1000 s or more,may indicate that lGRBs originate within binary systems.GRB 050904 could represent a rare case where the burst occurred in a binary system,leaving behind a black hole–black hole binary at redshift z=6.29.展开更多
In this paper,we present results from a semi-analytical model that investigates the launching of cold,nonrelativistic jets from a wide radial extent of stationary and axisymmetric magnetized accretion disks.Specifical...In this paper,we present results from a semi-analytical model that investigates the launching of cold,nonrelativistic jets from a wide radial extent of stationary and axisymmetric magnetized accretion disks.Specifically,we examine the effects of magnetization on the disk-jet system in configurations where the magnetic field is near equipartition with the thermal pressure at the disk midplane.In this study,the magnetic strength parameterμis explicitly expressed as a function of the magnetic diffusivity parameter(μ-1/√αm).This formulation provides a more direct link between the magnetic field configuration and the diffusive processes within the accretion disk.By establishing this relationship,we better constrain the role of magnetization in jet launching and explore how variations inμinfluence the overall disk-jet dynamics.We focus on three representative cases whereμtakes the values 0.5,0.7,and 0.9.We solve the stiff ordinary differential equations of the semi-analytical MHD model using the Seulex subroutine of Hairer&Wanner,which employs the Taylor method with adaptive mesh refinement.The resulting solutions are compared with those obtained by Zanni et al.,Tzeferacos et al.,and Stepanovs&Fendt.展开更多
For the general second order linear differential operator ■ with complex-valued distributional coefficients a_(jk), b_j, and c in an open set Ω ? R^n(n ≥ 1), we present conditions which ensure that-L^0 is accretive...For the general second order linear differential operator ■ with complex-valued distributional coefficients a_(jk), b_j, and c in an open set Ω ? R^n(n ≥ 1), we present conditions which ensure that-L^0 is accretive, i.e., Re<-L_0φ, φ >≥ 0 for all φ∈ C_0~∞(Ω).展开更多
A possible quasi-periodic oscillation(QPO) at frequency 7.045 × 10^(-5) Hz is found in the narrow-line Seyfert 1galaxy Mrk 142 in the data of XMM-Newton collected on 2020 April 11.We find that the QPO signal is s...A possible quasi-periodic oscillation(QPO) at frequency 7.045 × 10^(-5) Hz is found in the narrow-line Seyfert 1galaxy Mrk 142 in the data of XMM-Newton collected on 2020 April 11.We find that the QPO signal is statistically significantly larger than the 5σ level and highly coherent with quality factor Q > 5 at the 0.3–10 keV band by using the method of the Lomb–Scargle Periodogram,the Weighted Wavelet Z-transform and the REDFIT.We analyze the data in 0.3–0.6 keV,0.6–1 keV,1–3 keV and 3–10 keV energy bands,and find obvious QPO signals at 0.3–0.6 keV and 1–3 keV bands.We then analyze the time-average spectra and time variability at the QPO frequency of 7.045 × 10^(-5) Hz,and use a model to fit them.We find that the QPO signal mainly comes from the X-ray hot corona.展开更多
We present a comprehensive analysis of the 2021 outburst of MAXI J1803–298 utilizing observations of the Insight-Hard X-ray Modulation Telescope(Insight-HXMT)spanning from the low hard state to the high soft state.Wi...We present a comprehensive analysis of the 2021 outburst of MAXI J1803–298 utilizing observations of the Insight-Hard X-ray Modulation Telescope(Insight-HXMT)spanning from the low hard state to the high soft state.Within the Insight-HXMT data set,compared to the previous work,we identify a more prolonged presence of typeC quasi-periodic oscillations(QPOs)with centroid frequencies ranging from~0.16 to 6.3 Hz,which present correlations with the hardness ratio and the photon index of the Comptonized component.For QPO frequencies less than~2 Hz,the QPO phase lags are hard(photons of 10–19 keV arrive later than those of 1–4 keV),while at higher frequencies,the lags become soft at and above~4 Hz.Furthermore,the spectra in all Insight-HXMT observations consist of a multi-color blackbody component and a Comptonized component,as commonly observed in classical black hole X-ray binaries.We analyze state transitions and the evolution of accretion geometry in this work.The fitted inner disk radius increases abnormally during the low hard state,hypothesized to result from the corona condensing onto the inner disk.Additionally,two significant drops in flux are observed during the soft intermediate state,maybe implying changes in the corona/jet and the disk,respectively.展开更多
We investigate the observational appearance of static and spherically symmetric hairy black holes in the framework of gravitational decoupling with the weak energy condition(WEC). Two types of thin illumination condit...We investigate the observational appearance of static and spherically symmetric hairy black holes in the framework of gravitational decoupling with the weak energy condition(WEC). Two types of thin illumination conditions are studied: spherical accretion and disk accretion. As the hairy parameter increases, the size of the photon sphere and photon rings in both models decreases, and the overall luminosity attenuation becomes more pronounced. In spherical accretion, the luminosity of infalling accretion is significantly lower than that of stationary accretion. In disk accretion the luminosity of the black hole is contributed by direct emission, the lensing ring and the photon ring. Employing four types of astrophysical disk luminosity model,we investigate the appearance of halos and note that their luminosities do not superimpose when the source is on or beyond the innermost stable circular orbit.展开更多
River bank erosion is a natural process that occurs when the water flow of a river exceeds the bank’s ability to withstand it. It is a common phenomenon that causes extensive land damage, displacement of people, loss...River bank erosion is a natural process that occurs when the water flow of a river exceeds the bank’s ability to withstand it. It is a common phenomenon that causes extensive land damage, displacement of people, loss of crops, and infrastructure damage. The Gorai River, situated on the right bank of the Ganges, is a significant branch of the river that flows into the Bay of Bengal via the Mathumati and Baleswar rivers. The erosion of the banks of the Gorai River in Kushtia district is not a recent occurrence. Local residents have been dealing with this issue for the past hundred years, and according to the elderly members of the community, the erosion has become more severe activities. Therefore, the main objective of this research is to quantify river bank erosion and accretion and bankline shifting from 2003 to 2022 using multi-temporal Landsat images data with GIS and remote sensing technique. Bank-line migration occurs as a result of the interplay and interconnectedness of various factors such as the degree of river-related processes such as erosion, transportation, and deposition, the amount of water in the river during the high season, the geological and soil makeup, and human intervention in the river. The results show that the highest eroded area was 4.6 square kilometers during the period of 2016 to 2019, while the highest accreted area was 7.12 square kilometers during the period of 2013 to 2016. However, the erosion and accretion values fluctuated from year to year.展开更多
Soil organic carbon(C)sequestration and nitrogen(N)and phosphorus(P)burial were measured in two floodplain wetlands'soils of the West Fork of the White River watershed(Indiana,United States)whose catchments differ...Soil organic carbon(C)sequestration and nitrogen(N)and phosphorus(P)burial were measured in two floodplain wetlands'soils of the West Fork of the White River watershed(Indiana,United States)whose catchments differed in land use to better understand how land use practices affect wetland C and nutrient retention.The catchment of one floodplain,UpperWest Fork,is dominated by row crop agriculture(61%)whereas the second catchment,Beanblossom Creek,is mostly forested(85%).Soils(0-30cm)of the two floodplain wetlands had similar bulk density(1.23 g/cm^(3)).Soil organic C and N were low in both floodplains but the percent organic C and N was two times greater(3.3%C,0.22%N)in the agricultural floodplain than in the floodplain in the forested catchment(1.5%C,0.14%N).Soil P was three times greater in the agricultural(1100μg/g)than in the forested floodplain(350μg/g).Recent soil accretion based on ^(137)Cs which provides a historical record since 1964(60 years),was two times greater in the agricultural floodplain(2.2mm/year)than in the forested catchment(1.0mm/year).Sediment deposition(2500 g/m^(2)/year),C sequestration(90 g/m^(2)/year),and N burial(7.5g/m^(2)/year)were three times greater in the agricultural floodplain and P burial was seven times greater(3.0 vs.0.41 g/m^(2)/year).Long-term measurements(100 years)based on 210Pb did not show large differences in C sequestration and N burial between the two floodplains though soil accretion and sediment deposition were greater in the forested floodplain.We attribute these higher rates to greater erosion in the watershed before 1950 when the catchment had more agricultural land and before instruction on best management practices to reduce soil erosion.These findings confirm previously published studies that show that P enrichment and accumulation in floodplain soils represent legacy effects of agricultural land use in the catchment.展开更多
基金supported by the National Natural Science Foundation of China (grant Nos.12173048,12333004,11988101,and 12273057)the National Key R&D Program of China (No.2023YFA1607903)the support from the K.C.Wong Education Foundation。
文摘LB-1 is a binary system that has drawn great attention since its discovery in 2019.The two components of LB-1 are suggested to be a B-type star plus a black hole (BH).In this paper,we first calculate the wind mass-loss rate of the B-type star.We then calculate the mass capture rate by the BH,with which as the initial mass accretion rate,we calculate the truncation radius of the accretion disk and the corresponding emergent spectra of the accretion flow(comprising an inner advection-dominated accretion flow (ADAF)+an outer truncated accretion disk) within the framework of the disk evaporation model.It is found that the predicted truncation radius of the accretion disk with appropriate model parameters is consistent with observations inferred from the observed broad H_(α) emission line.The predicted X-ray luminosity is definitely below the estimated upper limits with the sensitivity of the Chandra X-ray Observatory of the X-ray luminosity≈2×10^(31)ergs^(-1),which is also consistent with observations.Finally,we argue that the disk evaporation model can indeed reflect the intrinsic physics of the accretion flow in LB-1,and has potential to be applied to other quiescent BHs in the future.
文摘Changes in the coastline are characterized by accretion and erosion. The aim of this study is to contribute to a better understanding of the dynamics of the coastline and the study areas with a view to mitigating and preventing the risk of coastal erosion in order to propose a coastal occupation model with planned development policies in the future. These phenomena lead to changes in the position of the coastline. After extraction, the satellite images are compiled, then superimposed and processed using Geographic Information Systems (GIS) for statistical calculation of coastline change rates. A morphosedimentary study is carried out using topography and sedimentology. The topographic method is used to calculate sediment volumes using monthly profiles. The sedimentological method is used to determine the granulometric variations in the morphological units by calculating sedimentological indices. With erosion rates of −2.13 m/yr and −2.17 m/yr respectively at Djiffère (Palmarin and Sangomar breccia) and Joal (Joal Fadhiouth and Ngazobil), the EPR index revealed a sediment deficit. Palmarin Ngallou and the island of Fadhiouth are undergoing accretion at rates of +1.43 m/yr and +1.14 m/yr respectively. From a topographical point of view, the respective accumulations of −13.74 m3/m of beach and −8.65 m3/m of beach at Djiffère and Joal respectively point to significant erosion on all the aerial beach units, while for the underwater beaches, accretion was noted with accumulations of +4.00 m3/m of beach and +5.94 m3/m at Djiffère and Joal respectively. As for the sedimentological results, the Mz index shows a decrease in grain size from the high beach to the surf zone. Some points show bimodal deposits, showing the impact of the dune on beach activity, confirmed by the dispersion on the Mz-sigma diagram. The three methods used in this work show that the Djiffère sector in Joal is dominated by erosion, even though accretion points can be noted.
文摘This paper investigates the star formation efficiency(SFE)of blue compact galaxies(BCGs)by analyzing various indicators,including(O II),(H_(α)),infrared emissions,and the 1.4 GHz radio continuum.The assessment of SFE was conducted using publicly accessible data that concentrated on star formation rates(SFRs)and depletion timescales.By employing the fundamental equation,I determined the SFE in relation to its freefall time,which highlighted variations in efficiencies associated with SFR masses derived from different spectra.The results demonstrated that the highest efficiency value was observed in the analysis of the 1.4 GHz radio continuum,emphasizing the importance of studying star-forming clouds across a range of electromagnetic wavelengths to achieve a comprehensive understanding of star formation mechanisms.The study's findings indicated a peak efficiency of star formation value of approximately 0.9%,while the relative minimum obtained from(O II)was around 0.42%,aligning with the range of SFEs documented in the existing literature.Additionally,investigating the factors that influence the variability in efficiency when examining clouds in BCGs across different wave bands is crucial for deepening our comprehension of the underlying processes of star formation.
基金supported by the National Key R&D Program of China(2023YFE0101200)supported by the National Key R&D Program of China(2021YFA0718500)+3 种基金Yunnan Revitalization Talent Support Program(Yun Ling Scholar Award)the National Natural Science Foundation of China(NSFC)grant 12393813the science research grants from the China Manned Space Projectsupported by Hunan Education Department Foundation(grant No.21A0096)。
文摘We conducted an analysis of the continuum during the onset and initial decline phases of the 2023 outburst in transient neutron star low-mass X-ray binary Aql X–1 using broadband observations from the Hard X-ray Modulation Telescope(Insight-HXMT)instrument.To determine the most appropriate model for the continuum of this outburst,we employed three models to explore the evolution of the spectral component.These observations revealed that the source transitions from the hard state to the soft state.The disk-corona and sphere-corona models both adequately described the spectra of the hard state,while the double blackbody model became preferable after the hard X-ray emission(>25 keV)disappeared during the state transition.In the soft state,the total emission is dominated by the accretion disk and two blackbody components.The combination of the sphere-corona model and the double blackbody model is the most suitable model for this outburst.The results suggest that as the source transitioned into the soft state,the emission from the boundary layer was enhanced,and a hot spot occurred.Notably,we identified two type-ⅠX-ray bursts,one of which exhibited a significant hard X-ray deficit(significance~4.82σ),which indicates that Insight-HXMT has the capability to capture the evolution of the corona in a single burst.
基金supported by the National Key R&D Program of China with grant No.2023YFA1608100supported by the National Natural Science Foundation of China(NSFC)under grant No.12273013+4 种基金support from the National Key R&D Program of China(grant Nos.2023YFA1607804,2022YFA1602902,and 2023YFA1607800)other NSFC projects(grant Nos.12120101003,12373010,12173051,and 12233008)the China Manned Space Project(No.CMS-CSST-2025-A06)the Strategic Priority Research Program of the Chinese Academy of Sciences with grant Nos.XDB0550100 and XDB0550000supported by the National Science Foundation under grant No.AST-2034437。
文摘Changing-look(CL)active galactic nuclei(AGNs)are an extremely rare type of AGNs,characterized by the appearance(turn-on)or disappearance(turn-off)of broad emission lines within months to years.We construct a sample of 211 CL AGN candidates by systematically searching the Sloan Digital Sky Survey spectra classified as GALAXY,but with the Zwicky Transient Facility and Near-Earth Object Wide-Field Infrared Explorer midinfrared light curves showing significant variability,at the redshift range from 0.1 to 0.75.To examine the success rate of this method,we cross-match the candidate sample with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope and the Dark Energy Spectroscopic Instrument for repeat spectra,finding that the success rate of this method is 50%.By incorporating previously reported CL AGNs,a total of 48 CL AGNs have been identified within our sample,including two recurrent CL AGNs newly confirmed in this work.Our results suggest that the typical rest-frame timescale of CL behavior is from 1.7 to 18.1 yr,which is inconsistent with the obscuration model,and the Eddington ratios of CL AGNs are about 0.01 in the bright state.Additionally,our CL AGN sample follows the M_(BH)–σ_(*)relation of quiescent galaxies.In the future,we expect to detect more galaxies turning into Type 1 AGNs in this CL AGN candidate sample.
基金supported by the National Natural Science Foundation of China(NSFC,Grant No.12073021)。
文摘We present simulation results examining the presence and behavior of standing shocks in zero-energy low angular momentum advective accretion flows and explore their(in)stability properties,taking into account various values of specific angular momentum,λ_(0).Within the range 10-50R_(g)(where R_(g)denotes the Schwarzschild radius),shocks are discernible forλ_(0)≥1.75.In the special relativistic hydrodynamic simulation whenλ_(0)=1.80,we find the merger of two shocks resulted in a dramatic increase in luminosity.We present the impact of external and internal flow collisions from the funnel region on luminosity.Notably,oscillatory behavior characterizes shocks within 1.70≤λ_(0)≤1.80.Using free–free emission as a proxy for analysis,we show that the luminosity oscillations between frequencies of 0.1-10 Hz forλ_(0)range as 1.7≤λ_(0)≤1.80.These findings offer insights into quasiperiodic oscillation emissions from certain black hole X-ray binaries,exemplified by GX 339-4.Furthermore,for the supermassive black hole at the Milky Way's center,Sgr A*,oscillation frequencies between 10^(-6)and 10^(-5)Hz were observed.This frequency range,translating to one cycle every few days,aligns with observational data from X-ray telescopes such as Chandra,Swift,and XMM-Newton.
文摘We present the results of a multi-epoch,detailed spectral and temporal analysis of the ultraluminous X-ray source(ULX),ULX-1,in the galaxy NGC 4088 using XMM-Newton,Chandra,and Swift observations.The presence of a hard powerlaw spectral slope supports the interpretation of ULX-1 as a hard ULX.The observed inner disk temperature of kT_(in)> 1.5 keV is inconsistent with the presence of an intermediate mass black hole,but favors the super-Eddington accretion state.Moreover,the physically acceptable value of the parameter controlling the radial temperature profile of the disk(p) derived from fitting the first XMM-Newton observation with the slim disk model further points towards the possible presence of a broadened disk,indicating the super-Eddington accretion nature.Slight overall long-term flux variability is evident for this ULX,and a hint towards a positive correlation between flux and the powerlaw photon index is also observed when the relatively better data of XMM-Newton and Chandra are considered.The L-T relationship is observed to follow a positive trend,with the L-T profile consistent with either relation(L ∝ T^(4) or L ∝ T^(2)) in both cases.The source exhibits no significant short-term variability at different time binnings of the light curve as indicated by the chi-square probability of constancy and fractional RMS variability values.The power density spectrum created shows no evidence of intrinsic variability of the source above the white noise.Further,no sign of pulsation was detected for this source.Assuming this ULX to be powered by an accreting black hole and using the slim disk geometry,the upper limit of the black hole mass was estimated and found to be less than 100M_(⊙).
基金supported by the National Natural Science Foundation of China(No.92371201)the State Key Laboratory for Strength and Vibration of Mechanical Structures Program,China.Thanks to China Aerodynamics Research and Development Center for providing the experimental data.
文摘The ice accretion on the wing surface of aircraft significantly impacts flight safety.Providing a precise safety assessment by examining flight characteristics and meteorological conditions is challenging.Based on different swept angles,the experimental data from the icing wind tunnel establish the geometric link between the position of the wingspan and the shape of ice accretion at the leading edge.The correlation analysis and Sobol sensitivity are used to study the uncertainty of single variable.Simultaneously,the polynomial chaos method is employed to study the uncertainty of multiple variables.The results indicate significant correlation between the angle of attack and lift and drag coefficients.The influence of height and velocity on sensitivity is negligible,with the aerodynamic characteristics mostly dependent on the geometric attributes of the ice structure.The uncertainty propagation framework established can accurately assess the impact of swept angle on the aerodynamic parameters of the icing wing,and the predicted findings fall within a 95%confidence interval.
文摘This study explores the dynamics of charged Hayward black holes,focusing on the effects of electric charge and the length factor on accretion disk characteristics.Our results show that increasing both parameters reduces the size of the event horizon and innermost stable circular orbits(ISCO)radius,with the electric charge exerting a more pronounced influence.Additionally,the length factor and electric charge can effectively replicate the spin of a Kerr black hole.Both parameters also affect the electromagnetic radiation emitted from the accretion disk,increasing the flux,temperature,and radiative efficiency.The peak radiation occurs in the soft x-ray band,with higher values of electric charge and length factor enhancing disk luminosity and shifting the peak to higher frequencies.These findings can offer valuable insights into the accretion processes around black holes and their observable signatures,particularly in x-ray astronomy.
基金supported by the National Natural Science Foundation of China(Grant No.U2241270)China Postdoctoral Science Foundation(Grant No.2025M774341)+1 种基金the Heilongjiang Province Postdoctoral Special Funding Project(Grant No.LBHTZ2408)the Outstanding Doctoral Dissertation Funding Project of Heilongjiang in the New Era(Grant No.LJYXL2024-007)。
文摘Polar ships face significant risks from ice accretion on decks,superstructures,and power systems.Ice formation on the power intake system particularly affects vessel stability and safety.While freshwater icing has been extensively researched,comprehensive multi-parameter studies on ice accretion for intake structures remain insufficient.This investigation examines the icing characteristics of the air shroud,a critical component of marine gas turbines,resulting from saltwater droplet freezing.The study utilized a custom-built cyclic ice wind tunnel,with flow field quality verified through Five-hole probe and Hot wire anemometer methods,and droplet field quality validated using Laser,Flowmeter,Ice blade,and Icing calibration grid techniques.The research analyzes ice distribution and thickness on the shroud under varying NaCl concentrations,considering temperature,liquid water content(LWC),and median volume diameter(MVD).The findings reveal that decreased salinity facilitates rime ice formation,resulting in rough ice texture.Temperature reduction,increased LWC,and larger MVD enhanced salinity's influence on ice thickness.The shroud exhibits substantial radial ice accretion,with coverage extending to approximately 90%.These results establish a foundation for further investigation of saltwater icing mechanisms and pioneer icing research in marine gas turbine intake systems.
文摘The mechanism of continental crust growth remains ambiguous.A key constraint is determining which tectonic settings were involved in the formation of the new continental crust.Because the basalts formed in intraplate(OIB,mean U/Pb=~0.37±0.11)and subduction(IAB,mean U/Pb=~0.10±0.06)settings have distinct U/Pb ratios,thus we back-calculate the present-day U/Pb ratios of the New Continental crust source[(U/Pb)_(nc)]based on our zircon-Hf and published whole rock-Pb isotope compositions of the WulagaⅠ-type granite to unfold the mechanism of the crust growth in the Lesser Xing'an Range(LXR),of the eastern Central Asian orogenic belt(CAOB).The Wulaga granodiorite porphyry yields zircon U-Pb ages of 103±1 Ma withε_(Hf)(t)of+6.0 to+9.0 and T_(DM2)of 590 to 784 Ma(averaging at 709±100 Ma).This result indicates that the Early Cretaceous Wulaga granodiorite porphyry was derived from the Neoproterozoic juvenile basaltic crust.The back-calculated(U/Pb)_(nc)values(0.15-0.18)may approximately represent the U/Pb ratios of the basaltic protolith of the Wulaga granite.It is similar to the U/Pb ratios in the IAB magmas within the calculation errors.Therefore,the crust growth of the LXR may occur through subduction at ca.700 Ma.In addition,this geochemical method also has been successfully applied to unfold the mechanism of the crust accretion of both the Jibei area in North China at ca.2.0 Ga and the Hongol area in the eastern CAOB during ca.1.1-0.8 Ga.The back-calculation of the present U/Pb ratio of the protolith ofⅠ-type granites in this study may constitute a potential method to constrain the mechanism of continental crustal accretion.
基金funding from the Department of Industrial Engineering,University of Naples FedericoⅡ,Italy。
文摘This study presents a data-driven approach to predict tailplane aerodynamics in icing conditions,supporting the ice-tolerant design of aircraft horizontal stabilizers.The core of this work is a low-cost predictive model for analyzing icing effects on swept tailplanes.The method relies on a multi-fidelity data gathering campaign,enabling seamless integration into multidisciplinary aircraft design workflows.A dataset of iced airfoil shapes was generated using 2D inviscid methods across various flight conditions.High-fidelity CFD simulations were conducted on both clean and iced geometries,forming a multidimensional aerodynamic database.This 2D database feeds a nonlinear vortex lattice method to estimate 3D aerodynamic characteristics,following a'quasi-3D'approach.The resulting reduced-order model delivers fast aerodynamic performance estimates of iced tailplanes.To demonstrate its effectiveness,optimal ice-tolerant tailplane designs were selected from a range of feasible shapes based on a reference transport aircraft.The analysis validates the model's reliability,accuracy,and limitations concerning 3D ice shapes and aerodynamic characteristics.Most notably,the model offers near-zero computational cost compared to high-fidelity simulations,making it a valuable tool for efficient aircraft design.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(grant No.XDB0550400)the National Key Research and Development Program of China(Nos.2024YFA1611704 and 2021YFA0718500)the National Natural Science Foundation of China(NSFC,Nos.12473049,12041301,12121003,and 12225305).
文摘Most massive stars reside in binary or multi-object systems.Short gamma-ray bursts(sGRBs),the product of the merger of double compact objects,may originate from massive common-envelope binaries.In contrast,the progenitors of long GRBs(lGRBs)are typically considered isolated massive stars.However,no effective method has yet been established to identify potential companions from current observations.Recent studies have demonstrated that quasi-periodic oscillation signatures can serve as a promising tool to probe the properties of GRB central engines.In this study,by drawing an analogy to periodicity in X-ray binaries,we explore the precession periods of companion-induced disk precession for lGRBs born in the ultra-compact binary scenario.Our results suggest that the periodicity observed in lGRB afterglows,measured in units of 1000 s or more,may indicate that lGRBs originate within binary systems.GRB 050904 could represent a rare case where the burst occurred in a binary system,leaving behind a black hole–black hole binary at redshift z=6.29.
文摘In this paper,we present results from a semi-analytical model that investigates the launching of cold,nonrelativistic jets from a wide radial extent of stationary and axisymmetric magnetized accretion disks.Specifically,we examine the effects of magnetization on the disk-jet system in configurations where the magnetic field is near equipartition with the thermal pressure at the disk midplane.In this study,the magnetic strength parameterμis explicitly expressed as a function of the magnetic diffusivity parameter(μ-1/√αm).This formulation provides a more direct link between the magnetic field configuration and the diffusive processes within the accretion disk.By establishing this relationship,we better constrain the role of magnetization in jet launching and explore how variations inμinfluence the overall disk-jet dynamics.We focus on three representative cases whereμtakes the values 0.5,0.7,and 0.9.We solve the stiff ordinary differential equations of the semi-analytical MHD model using the Seulex subroutine of Hairer&Wanner,which employs the Taylor method with adaptive mesh refinement.The resulting solutions are compared with those obtained by Zanni et al.,Tzeferacos et al.,and Stepanovs&Fendt.
文摘For the general second order linear differential operator ■ with complex-valued distributional coefficients a_(jk), b_j, and c in an open set Ω ? R^n(n ≥ 1), we present conditions which ensure that-L^0 is accretive, i.e., Re<-L_0φ, φ >≥ 0 for all φ∈ C_0~∞(Ω).
基金financial supports from the Science Foundation of Department of Education of Yunnan Province (2024J0935)。
文摘A possible quasi-periodic oscillation(QPO) at frequency 7.045 × 10^(-5) Hz is found in the narrow-line Seyfert 1galaxy Mrk 142 in the data of XMM-Newton collected on 2020 April 11.We find that the QPO signal is statistically significantly larger than the 5σ level and highly coherent with quality factor Q > 5 at the 0.3–10 keV band by using the method of the Lomb–Scargle Periodogram,the Weighted Wavelet Z-transform and the REDFIT.We analyze the data in 0.3–0.6 keV,0.6–1 keV,1–3 keV and 3–10 keV energy bands,and find obvious QPO signals at 0.3–0.6 keV and 1–3 keV bands.We then analyze the time-average spectra and time variability at the QPO frequency of 7.045 × 10^(-5) Hz,and use a model to fit them.We find that the QPO signal mainly comes from the X-ray hot corona.
基金supported by the National Key R&D Program of China(2021YFA0718500)the National Natural Science Foundation of China(NSFC,Grant No.12133007)partially supported by the International Partnership Program of Chinese Academy of Sciences(Grant No.113111KYSB20190020)。
文摘We present a comprehensive analysis of the 2021 outburst of MAXI J1803–298 utilizing observations of the Insight-Hard X-ray Modulation Telescope(Insight-HXMT)spanning from the low hard state to the high soft state.Within the Insight-HXMT data set,compared to the previous work,we identify a more prolonged presence of typeC quasi-periodic oscillations(QPOs)with centroid frequencies ranging from~0.16 to 6.3 Hz,which present correlations with the hardness ratio and the photon index of the Comptonized component.For QPO frequencies less than~2 Hz,the QPO phase lags are hard(photons of 10–19 keV arrive later than those of 1–4 keV),while at higher frequencies,the lags become soft at and above~4 Hz.Furthermore,the spectra in all Insight-HXMT observations consist of a multi-color blackbody component and a Comptonized component,as commonly observed in classical black hole X-ray binaries.We analyze state transitions and the evolution of accretion geometry in this work.The fitted inner disk radius increases abnormally during the low hard state,hypothesized to result from the corona condensing onto the inner disk.Additionally,two significant drops in flux are observed during the soft intermediate state,maybe implying changes in the corona/jet and the disk,respectively.
基金supported by the National Natural Science Foundation of China (NSFC) with grant nos 12175212, 12275183 and 12275184。
文摘We investigate the observational appearance of static and spherically symmetric hairy black holes in the framework of gravitational decoupling with the weak energy condition(WEC). Two types of thin illumination conditions are studied: spherical accretion and disk accretion. As the hairy parameter increases, the size of the photon sphere and photon rings in both models decreases, and the overall luminosity attenuation becomes more pronounced. In spherical accretion, the luminosity of infalling accretion is significantly lower than that of stationary accretion. In disk accretion the luminosity of the black hole is contributed by direct emission, the lensing ring and the photon ring. Employing four types of astrophysical disk luminosity model,we investigate the appearance of halos and note that their luminosities do not superimpose when the source is on or beyond the innermost stable circular orbit.
文摘River bank erosion is a natural process that occurs when the water flow of a river exceeds the bank’s ability to withstand it. It is a common phenomenon that causes extensive land damage, displacement of people, loss of crops, and infrastructure damage. The Gorai River, situated on the right bank of the Ganges, is a significant branch of the river that flows into the Bay of Bengal via the Mathumati and Baleswar rivers. The erosion of the banks of the Gorai River in Kushtia district is not a recent occurrence. Local residents have been dealing with this issue for the past hundred years, and according to the elderly members of the community, the erosion has become more severe activities. Therefore, the main objective of this research is to quantify river bank erosion and accretion and bankline shifting from 2003 to 2022 using multi-temporal Landsat images data with GIS and remote sensing technique. Bank-line migration occurs as a result of the interplay and interconnectedness of various factors such as the degree of river-related processes such as erosion, transportation, and deposition, the amount of water in the river during the high season, the geological and soil makeup, and human intervention in the river. The results show that the highest eroded area was 4.6 square kilometers during the period of 2016 to 2019, while the highest accreted area was 7.12 square kilometers during the period of 2013 to 2016. However, the erosion and accretion values fluctuated from year to year.
文摘Soil organic carbon(C)sequestration and nitrogen(N)and phosphorus(P)burial were measured in two floodplain wetlands'soils of the West Fork of the White River watershed(Indiana,United States)whose catchments differed in land use to better understand how land use practices affect wetland C and nutrient retention.The catchment of one floodplain,UpperWest Fork,is dominated by row crop agriculture(61%)whereas the second catchment,Beanblossom Creek,is mostly forested(85%).Soils(0-30cm)of the two floodplain wetlands had similar bulk density(1.23 g/cm^(3)).Soil organic C and N were low in both floodplains but the percent organic C and N was two times greater(3.3%C,0.22%N)in the agricultural floodplain than in the floodplain in the forested catchment(1.5%C,0.14%N).Soil P was three times greater in the agricultural(1100μg/g)than in the forested floodplain(350μg/g).Recent soil accretion based on ^(137)Cs which provides a historical record since 1964(60 years),was two times greater in the agricultural floodplain(2.2mm/year)than in the forested catchment(1.0mm/year).Sediment deposition(2500 g/m^(2)/year),C sequestration(90 g/m^(2)/year),and N burial(7.5g/m^(2)/year)were three times greater in the agricultural floodplain and P burial was seven times greater(3.0 vs.0.41 g/m^(2)/year).Long-term measurements(100 years)based on 210Pb did not show large differences in C sequestration and N burial between the two floodplains though soil accretion and sediment deposition were greater in the forested floodplain.We attribute these higher rates to greater erosion in the watershed before 1950 when the catchment had more agricultural land and before instruction on best management practices to reduce soil erosion.These findings confirm previously published studies that show that P enrichment and accumulation in floodplain soils represent legacy effects of agricultural land use in the catchment.
