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  • Isospin equilibration in multinucleon transfer reaction at near-barrier energies

    分类: 物理学 >> 核物理学 提交时间: 2023-06-23

    摘要: 系统测试

  • Relating galaxies across different redshift to study galaxy evolution

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We propose a general framework leveraging the halo-galaxy connection to link galaxies observed at different redshift in a statistical way, and use the link to infer the redshift evolution of the galaxy population. Our tests based on hydrodynamic simulations show that our method can accurately recover the stellar mass assembly histories up to $z\sim 3$ for present star-forming and quiescent galaxies down to $10^{10}h^{-1}M_{\odot}$. Applying the method to observational data shows that the stellar mass evolution of the main progenitors of galaxies depends strongly on the properties of descendants, such as stellar mass, halo mass, and star formation states. Galaxies hosted by low-mass groups/halos at the present time have since $z\sim 1.8$ grown their stellar mass $\sim 2.5$ times as fast as those hosted by massive clusters. This dependence on host halo mass becomes much weaker for descendant galaxies with similar star formation states. Star-forming galaxies grow about 2-4 times faster than their quiescent counterparts since $z\sim 1.8$. Both TNG and EAGLE simulations over-predict the progenitor stellar mass at $z>1$, particularly for low-mass descendants.

  • A simulation experiment of a pipeline based on machine learning for neutral hydrogen intensity mapping surveys

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We present a simulation experiment of a pipeline based on machine learning algorithms for neutral hydrogen (HI) intensity mapping (IM) surveys with different telescopes. The simulation is conducted on HI signals, foreground emission, thermal noise from instruments, strong radio frequency interference (sRFI), and mild RFI (mRFI). We apply the Mini-Batch K-Means algorithm to identify sRFI, and Adam algorithm to remove foregrounds and mRFI. Results show that there exists a threshold of the sRFI amplitudes above which the performance of our pipeline enhances greatly. In removing foregrounds and mRFI, the performance of our pipeline is shown to have little dependence on the apertures of telescopes. In addition, the results show that there are thresholds of the signal amplitudes from which the performance of our pipeline begins to change rapidly. We consider all these thresholds as the edges of the signal amplitude ranges in which our pipeline can function well. Our work, for the first time, explores the feasibility of applying machine learning algorithms in the pipeline of IM surveys, especially for large surveys with the next-generation telescopes.

  • Relating galaxies across different redshift to study galaxy evolution

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We propose a general framework leveraging the halo-galaxy connection to link galaxies observed at different redshift in a statistical way, and use the link to infer the redshift evolution of the galaxy population. Our tests based on hydrodynamic simulations show that our method can accurately recover the stellar mass assembly histories up to $z\sim 3$ for present star-forming and quiescent galaxies down to $10^{10}h^{-1}M_{\odot}$. Applying the method to observational data shows that the stellar mass evolution of the main progenitors of galaxies depends strongly on the properties of descendants, such as stellar mass, halo mass, and star formation states. Galaxies hosted by low-mass groups/halos at the present time have since $z\sim 1.8$ grown their stellar mass $\sim 2.5$ times as fast as those hosted by massive clusters. This dependence on host halo mass becomes much weaker for descendant galaxies with similar star formation states. Star-forming galaxies grow about 2-4 times faster than their quiescent counterparts since $z\sim 1.8$. Both TNG and EAGLE simulations over-predict the progenitor stellar mass at $z>1$, particularly for low-mass descendants.

  • Idealized 2D Cloud-Resolving Simulations for Tidally Locked Habitable Planets

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Cloud is critical for planetary climate and habitability, but it is also one of the most challenging parts of studying planets in and beyond the solar system. Here we use a cloud-resolving model (CRM) with high resolution (2 km) in a two-dimensional (2D) configuration to simulate the clouds and circulation on tidally locked aqua-planets. We find that the substellar area is covered by deep convective clouds, the nightside is dominated by low-level clouds, and these two are linked by a global-scale Walker circulation. We further find that a uniform surface warming causes the substellar cloud width to decrease, but a reduction in day-night surface temperature contrast or an increase in longwave radiative cooling rate causes the substellar cloud width to increase. These relationships can be roughly interpreted based on simple thermodynamic theories. Comparing the results between CRM and global 3D general circulation model (GCM), we find that they show qualitatively consistent results, including the Walker circulation, the substellar clouds, and the responses of the substellar ascending area and strength to changes in surface temperature or in its zonal contrast. But, large quantitative differences exist, such as the magnitude of cloud water path, the cloud width, and their responses to external forcings. These results increase our confidence in using GCMs for modeling exoplanetary climates, although large quantitative uncertainties should always exist. Future work is required to use 3D CRM(s) with realistic radiative transfer and with the Coriolis force to examine the clouds and climate of tidally locked planets.

  • Finding proto-clusters to trace galaxy evolution: I. The finder and its performance

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We develop a method to identify proto-clusters based on dark matter halos represented by galaxy groups selected from surveys of galaxies at high redshift. We test the performance of this method on halos in N-body simulations, and find it can correctly identify more than 85% of the true proto-clusters with $\gtrsim$ 95% purity and with mass estimates typical within 0.25 dex from their true values. We show how the information provided by the proto-clusters can be used to link galaxies in present-day clusters of galaxies with their high redshift progenitors. Our tests show that the proto-clusters identified by our method can recover reliably the progenitor stellar mass distribution of galaxies, thereby providing an avenue to investigate the formation and evolution of present-day galaxy clusters and their member galaxies.

  • Conditional HI mass functions and the HI-to-halo mass relation in the local Universe

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We present a new HI mass estimator which relates the HI-to-stellar mass ratio to four galaxy properties: stellar surface mass density, color index $u-r$, stellar mass and concentration index, with the scatter of individual galaxies around the mean HI mass modeled with a Gaussian distribution. We calibrate the estimator using the xGASS sample, including both HI detection and non-detection, and constrain the model parameters through Bayesian inferences. Tests with mock catalogs demonstrate that our estimator provides unbiased HI masses for optical samples like the SDSS, thus suitable for statistical studies of HI gas contents in galaxies and dark matter halos. We apply our estimator to the SDSS spectroscopic sample to estimate the local HI mass function (HIMF), the conditional HI mass function (CHIMF) in galaxy groups and the HI-halo mass (HIHM) relation. Our HIMF agrees with the ALFALFA measurements at $M_{HI}\gtrsim 5\times 10^9M_{\odot}$, but with higher amplitude and a steeper slope at lower masses. We show that this discrepancy is caused primarily by the cosmic variance which is corrected for the SDSS sample but not for the ALFALFA. The CHIMFs for all halo masses can be described by a single Schechter function, and this is true for red, blue and satellite galaxies. For central galaxies the CHIMFs show a double-Gaussian profile, with the two components contributed by the red and blue galaxies, respectively. The total HI mass in a group increases monotonically with halo mass. The HI mass of central galaxies in galaxy groups increases rapidly with halo mass only at $M_h\lesssim10^{12}M_{\odot}$, while the mass dependence becomes much weaker at higher halo masses. The observed HI-halo mass relation is not reproduced by current hydrodynamic simulations and semi-analytic models of galaxy formation.

  • Galaxy populations in groups and clusters: evidence for a characteristic stellar mass scale at $M_\ast\sim 10^{9.5}M_\odot$

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We use the most recent data release (DR9) of the DESI legacy imaging survey and SDSS galaxy groups to measure the conditional luminosity function (CLF) for groups with halo mass $M_{\rm h}\ge 10^{12}M_{\odot}$ and redshift $0.01\le z\le 0.08$, down to a limiting $r$-band magnitude of $M_{\rm r}=-10\sim-12$. For a given halo mass we measure the CLF for the total satellite population, as well as separately for the red and blue populations classified using the $(g-z)$ color. We find a clear faint-end upturn in the CLF of red satellites, with a slope $\alpha\approx-1.8$ which is almost independent of halo mass. This faint-end upturn is not seen for blue satellites and for the total population. Our stellar population synthesis modeling shows that the $(g-z)$ color provides a clean red/blue division, and that group galaxies in the red population defined by $(g-z)$ are all dominated by old stellar populations. The fraction of old galaxies as a function of galaxy luminosity shows a minimum at a luminosity $M_{\rm r}\sim-18$, corresponding to a stellar mass $M_\ast\sim10^{9.5}M_\odot$. This mass scale is independent of halo mass and is comparable to the characteristic luminosity at which galaxies show a dichotomy in surface brightness and size, suggesting that the dichotomy in the old fraction and in galaxy structure may have a common origin. The rising of the old fraction at the faint end for Milky Way (MW)-sized halos found here is in good agreement with the quenched fraction measured both for the MW/M31 system and from the ELVES survey. We discuss the implications of our results for the formation and evolution of low-mass galaxies, and for the stellar mass functions of low-mass galaxies to be observed at high redshift.

  • Quasinormal-modes of the Kerr-Newman black hole: GW150914 and fundamental physics implications

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We develop an analytical ringdown waveform model, including both the fundamental and the overtone quasinormal modes, for charged black holes and show that it is precise enough to analyze current gravitational wave data. Applying this waveform model to GW150914, the charge to mass ratio of the remnant black hole ($\lambda_f$) has been constrained with the sole ringdown gravitational wave data for the first time and the $90\%$ upper limit is $\lambda_f\leq 0.38$. Correspondingly, the deviation parameter of the scalar-tensor vector gravity ($\alpha_{\rm s}$) is limited to be $\alpha_{\rm s}\leq 0.17$. Our approach can be directly applied to other binary black hole mergers with loud ringdown radiation.

  • Galaxy populations in groups and clusters: evidence for a characteristic stellar mass scale at $M_\ast\sim 10^{9.5}M_\odot$

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We use the most recent data release (DR9) of the DESI legacy imaging survey and SDSS galaxy groups to measure the conditional luminosity function (CLF) for groups with halo mass $M_{\rm h}\ge 10^{12}M_{\odot}$ and redshift $0.01\le z\le 0.08$, down to a limiting $r$-band magnitude of $M_{\rm r}=-10\sim-12$. For a given halo mass we measure the CLF for the total satellite population, as well as separately for the red and blue populations classified using the $(g-z)$ color. We find a clear faint-end upturn in the CLF of red satellites, with a slope $\alpha\approx-1.8$ which is almost independent of halo mass. This faint-end upturn is not seen for blue satellites and for the total population. Our stellar population synthesis modeling shows that the $(g-z)$ color provides a clean red/blue division, and that group galaxies in the red population defined by $(g-z)$ are all dominated by old stellar populations. The fraction of old galaxies as a function of galaxy luminosity shows a minimum at a luminosity $M_{\rm r}\sim-18$, corresponding to a stellar mass $M_\ast\sim10^{9.5}M_\odot$. This mass scale is independent of halo mass and is comparable to the characteristic luminosity at which galaxies show a dichotomy in surface brightness and size, suggesting that the dichotomy in the old fraction and in galaxy structure may have a common origin. The rising of the old fraction at the faint end for Milky Way (MW)-sized halos found here is in good agreement with the quenched fraction measured both for the MW/M31 system and from the ELVES survey. We discuss the implications of our results for the formation and evolution of low-mass galaxies, and for the stellar mass functions of low-mass galaxies to be observed at high redshift.

  • Mapping dust attenuation and the 2175 {\AA} bump at kpc scales in nearby galaxies

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We develop a novel approach to measure dust attenuation properties of galaxies,including the dust opacity and shape of the attenuation curve in both optical and NUV, as well as the strength of the 2175{\AA} absorption feature. From an observed spectrum the method uses a model-independent approach to derive a relative attenuation curve.The absolute amplitude is then calibrated with the NIR photometry. The dust-corrected spectrum is fitted with stellar population models to derive the dust-free model spectrum covering the whole wavelength range from NUV to NIR and is compared with the observed SED/spectrum to determine dust attenuation properties. We apply this method to investigate dust attenuation on kpc scales, using a sample of 134 galaxies with the integral field spectroscopy from MaNGA, the NIR imaging from 2MASS, and the NUV imaging from Swift/UVOT. We find that the attenuation curves in regions of kpc scales span a wide range of slopes in both optical and UV. The slope is shallower at higher optical opacity, a trend that is held even when the sample is limited to narrow ranges of specific star formation rate (sSFR), minor-to-major axis ratio (b/a) and the location within individual galaxies. The 2175{\AA} bump in the attenuation curve at kpc scales presents a wide range of strength. The strength shows a strong negative correlation with the sSFR, but the correlations with the optical opacity, $b/a$ and the location within individual galaxies are all weak. All these trends appear to be independent of the stellar mass of galaxies, implying that the dust attenuation is regulated by local processes rather than by global properties of galaxies. Our results support the scenario that the variation of the 2175{\AA} bump is driven predominantly by processes related to star formation, such as destruction of small dust grains by UV radiation in star-forming regions.

  • Mapping dust attenuation and the 2175 {\AA} bump at kpc scales in nearby galaxies

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We develop a novel approach to measure dust attenuation properties of galaxies,including the dust opacity and shape of the attenuation curve in both optical and NUV, as well as the strength of the 2175{\AA} absorption feature. From an observed spectrum the method uses a model-independent approach to derive a relative attenuation curve.The absolute amplitude is then calibrated with the NIR photometry. The dust-corrected spectrum is fitted with stellar population models to derive the dust-free model spectrum covering the whole wavelength range from NUV to NIR and is compared with the observed SED/spectrum to determine dust attenuation properties. We apply this method to investigate dust attenuation on kpc scales, using a sample of 134 galaxies with the integral field spectroscopy from MaNGA, the NIR imaging from 2MASS, and the NUV imaging from Swift/UVOT. We find that the attenuation curves in regions of kpc scales span a wide range of slopes in both optical and UV. The slope is shallower at higher optical opacity, a trend that is held even when the sample is limited to narrow ranges of specific star formation rate (sSFR), minor-to-major axis ratio (b/a) and the location within individual galaxies. The 2175{\AA} bump in the attenuation curve at kpc scales presents a wide range of strength. The strength shows a strong negative correlation with the sSFR, but the correlations with the optical opacity, $b/a$ and the location within individual galaxies are all weak. All these trends appear to be independent of the stellar mass of galaxies, implying that the dust attenuation is regulated by local processes rather than by global properties of galaxies. Our results support the scenario that the variation of the 2175{\AA} bump is driven predominantly by processes related to star formation, such as destruction of small dust grains by UV radiation in star-forming regions.

  • Conditional HI mass functions and the HI-to-halo mass relation in the local Universe

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We present a new HI mass estimator which relates the HI-to-stellar mass ratio to four galaxy properties: stellar surface mass density, color index $u-r$, stellar mass and concentration index, with the scatter of individual galaxies around the mean HI mass modeled with a Gaussian distribution. We calibrate the estimator using the xGASS sample, including both HI detection and non-detection, and constrain the model parameters through Bayesian inferences. Tests with mock catalogs demonstrate that our estimator provides unbiased HI masses for optical samples like the SDSS, thus suitable for statistical studies of HI gas contents in galaxies and dark matter halos. We apply our estimator to the SDSS spectroscopic sample to estimate the local HI mass function (HIMF), the conditional HI mass function (CHIMF) in galaxy groups and the HI-halo mass (HIHM) relation. Our HIMF agrees with the ALFALFA measurements at $M_{HI}\gtrsim 5\times 10^9M_{\odot}$, but with higher amplitude and a steeper slope at lower masses. We show that this discrepancy is caused primarily by the cosmic variance which is corrected for the SDSS sample but not for the ALFALFA. The CHIMFs for all halo masses can be described by a single Schechter function, and this is true for red, blue and satellite galaxies. For central galaxies the CHIMFs show a double-Gaussian profile, with the two components contributed by the red and blue galaxies, respectively. The total HI mass in a group increases monotonically with halo mass. The HI mass of central galaxies in galaxy groups increases rapidly with halo mass only at $M_h\lesssim10^{12}M_{\odot}$, while the mass dependence becomes much weaker at higher halo masses. The observed HI-halo mass relation is not reproduced by current hydrodynamic simulations and semi-analytic models of galaxy formation.

  • A Conditional Abundance Matching Method of Extending Simulated Halo Merger Trees to Resolve Low-Mass Progenitors and Sub-halos

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We present an algorithm to extend subhalo merger trees in a low-resolution dark-matter-only simulation by conditionally matching them to those in a high-resolution simulation. The algorithm is general and can be applied to simulation data with different resolutions using different target variables. We instantiate the algorithm by a case in which trees from ELUCID, a constrained simulation of $(500h^{-1}{\rm Mpc})^3$ volume of the local universe, are extended by matching trees from TNGDark, a simulation with much higher resolution. Our tests show that the extended trees are statistically equivalent to the high-resolution trees in the joint distribution of subhalo quantities and in important summary statistics relevant to modeling galaxy formation and evolution in halos. The extended trees preserve certain information of individual systems in the target simulation, including properties of resolved satellite subhalos, and shapes and orientations of their host halos. With the extension, subhalo merger trees in a cosmological scale simulation are extrapolated to a mass resolution comparable to that in a higher-resolution simulation carried out in a smaller volume, which can be used as the input for (sub)halo-based models of galaxy formation. The source code of the algorithm, and halo merger trees extended to a mass resolution of $\sim 2 \times 10^8 h^{-1}M_\odot$ in the entire ELUCID simulation, are available.

  • A Conditional Abundance Matching Method of Extending Simulated Halo Merger Trees to Resolve Low-Mass Progenitors and Sub-halos

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We present an algorithm to extend subhalo merger trees in a low-resolution dark-matter-only simulation by conditionally matching them to those in a high-resolution simulation. The algorithm is general and can be applied to simulation data with different resolutions using different target variables. We instantiate the algorithm by a case in which trees from ELUCID, a constrained simulation of $(500h^{-1}{\rm Mpc})^3$ volume of the local universe, are extended by matching trees from TNGDark, a simulation with much higher resolution. Our tests show that the extended trees are statistically equivalent to the high-resolution trees in the joint distribution of subhalo quantities and in important summary statistics relevant to modeling galaxy formation and evolution in halos. The extended trees preserve certain information of individual systems in the target simulation, including properties of resolved satellite subhalos, and shapes and orientations of their host halos. With the extension, subhalo merger trees in a cosmological scale simulation are extrapolated to a mass resolution comparable to that in a higher-resolution simulation carried out in a smaller volume, which can be used as the input for (sub)halo-based models of galaxy formation. The source code of the algorithm, and halo merger trees extended to a mass resolution of $\sim 2 \times 10^8 h^{-1}M_\odot$ in the entire ELUCID simulation, are available.

  • Star formation histories of massive red spiral galaxies in the local universe

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We investigate the star formation histories (SFHs) of massive red spiral galaxies with stellar mass $M_\ast>10^{10.5}M_\odot$, and make comparisons with blue spirals and red ellipticals of similar masses. We make use of the integral field spectroscopy from the SDSS-IV/DR15 MaNGA sample, and estimate spatially resolved SFHs and stellar population properties of each galaxy by applying a Bayesian spectral fitting code to the MaNGA spectra. We find that both red spirals and red ellipticals have experienced only one major star formation episode at early times, and the result is independent of the adopted SFH model. On average, more than half of their stellar masses were formed $>$10 Gyrs ago, and more than 90\% were formed $>6$ Gyrs ago. The two types of galaxies show similarly flat profiles in a variety of stellar population parameters: old stellar ages indicated by $D4000$ (the spectral break at around 4000\AA), high stellar metallicities, large Mgb/Fe ratios indicating fast formation, and little stellar dust attenuation. In contrast, although blue spirals also formed their central regions $>$10 Gyrs ago, both their central regions and outer disks continuously form stars over a long timescale. Our results imply that, massive red spirals are likely to share some common processes of formation (and possibly quenching) with massive red ellipticals in the sense that both types were formed at $z > 2$ through a fast formation process.Possible mechanisms for the formation and quenching of massive red spirals are discussed.

  • Wolf-Rayet galaxies in SDSS-IV MaNGA. II. Metallicity dependence of the high-mass slope of the stellar initial mass function

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: As hosts of living high-mass stars, Wolf-Rayet (WR) regions or WR galaxies are ideal objects for constraining the high-mass end of the stellar initial mass function (IMF). We construct a large sample of 910 WR galaxies/regions that cover a wide range of stellar metallicity (from Z~0.001 up to Z~0.03), by combining three catalogs of WR galaxies/regions previously selected from the SDSS and SDSS-IV/MaNGA surveys. We measure the equivalent widths of the WR blue bump at ~4650 A for each spectrum. They are compared with predictions from stellar evolutionary models Starburst99 and BPASS, with different IMF assumptions (high-mass slope {\alpha} of the IMF ranging from 1.0 up to 3.3). Both singular evolution and binary evolution are considered. We also use a Bayesian inference code to perform full spectral fitting to WR spectra with stellar population spectra from BPASS as fitting templates. We then make model selection among different {\alpha} assumptions based on Bayesian evidence. These analyses have consistently led to a positive correlation of IMF high-mass slope {\alpha} with stellar metallicity Z, i.e. with steeper IMF (more bottom-heavy) at higher metallicities. Specifically, an IMF with {\alpha}=1.00 is preferred at the lowest metallicity (Z~0.001), and a Salpeter or even steeper IMF is preferred at the highest metallicity (Z~0.03). These conclusions hold even when binary population models are adopted.

  • MAHGIC: A Model Adapter for the Halo-Galaxy Inter-Connection

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: We develop a model to establish the interconnection between galaxies and their dark matter halos. We use Principal Component Analysis (PCA) to reduce the dimensionality of both the mass assembly histories of halos/subhalos and the star formation histories of galaxies, and Gradient Boosted Decision Trees (GBDT) to transform halo/subhalo properties into galaxy properties. We use two sets of hydrodynamic simulations to motivate our model architecture and to train the transformation. We then apply the two sets of trained models to dark matter only (DMO) simulations to show that the transformation is reliable and statistically accurate. The model trained by a high-resolution hydrodynamic simulation, or by a set of such simulations implementing the same physics of galaxy formation, can thus be applied to large DMO simulations to make "mock" copies of the hydrodynamic simulation. The model is both flexible and interpretable, which paves the way for future applications in which we will constrain the model using observations at different redshifts simultaneously and explore how galaxies form and evolve in dark matter halos empirically.

  • Efficient and selective removal of Pb(II) from landfill leachate using L-serine-modified polyethylene/polypropylene nonwoven fabric synthesized via radiation grafting technique

    分类: 核科学技术 >> 核科学技术其他学科 提交时间: 2024-05-08

    摘要: In this study, to efficiently remove Pb(II) from aqueous environments, a novel L-serine-modified polyethylene/polypropylene nonwoven fabric sorbent (NWF-serine) was fabricated through the radiation grafting of glycidyl methacrylate and subsequent L-serine modification. The effect of the absorbed dose was investigated in the range of 5–50 kGy. NWF-serine was characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Batch adsorption tests were conducted to investigate the influences of pH, adsorption time, temperature, initial concentration, and sorbent dosage on the Pb(II) adsorption performance of NWF-serine. The results indicated that Pb(II) adsorption onto NWF-serine was an endothermic process, following the pseudo-second-order kinetic model and Langmuir isotherm model. The saturated adsorption capacity was 198.1 mg/g. NWF-serine exhibited Pb(II) removal rates of 99.8% for aqueous solutions with initial concentrations of 100 mg/L and 82.1% for landfill leachate containing competitive metal ions such as Cd, Cu, Ni, Mn, and Zn. Furthermore, NWF-serine maintained 86% of its Pb(II) uptake after five use cycles. The coordination of the carboxyl and amino groups with Pb(II) was confirmed using X-ray photoelectron spectroscopy and extended X-ray absorption fine structure analysis.

  • Seasonal variations of chemical species and haze in Titan's upper atmosphere

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Seasonal variation is significant in Titan's atmosphere due to the large change of solar insolation resulting from Titan's 26.7{\deg} axial tilt relative to the plane of Saturn's orbit. Here we present an investigation of hydrocarbon and nitrile species in Titan's upper atmosphere at 400-1200 km, which includes the mesosphere and the lower thermosphere, over more than one fourth of Titan's year (2006-2014, LS=318{\deg}-60{\deg}), using eighteen stellar occultation observations obtained by Cassini/UVIS. Vertical profiles of eight chemical species (CH4, C2H2, C2H4, C2H6, C4H2, C6H6, HCN, HC3N) and haze particles are retrieved from these observations using an instrument forward model, which considers the technical issue of pointing motion. The Markov-chain Monte Carlo (MCMC) algorithm is used to obtain the posterior probability distributions of parameters in the retrieval, which inherently tests the extent to which species profiles can be constrained. The results show that no change of the species profiles is noticeable before the equinox, while the decrease of atmospheric temperature and significant upwelling in the summer hemisphere are found five terrestrial years afterwards. Altitude of the detached haze layer decreases towards the vernal equinox then it disappears, and no reappearance is identified within the time range of our data, which is consistent with observations from Cassini/ISS. This study provides observational constraints on the seasonal change of Titan's upper atmosphere, and suggests further investigations of the atmospheric chemistry and dynamics therein.