分类： 生物学 >> 动物学 提交时间： 2019-06-11 合作期刊: 《古脊椎动物学报》
摘要： The late-branching alvarezsaurian Xixianykus zhangi is among the smallest known non-avialan theropods. With great similarity to its close relatives, it is highly cursorial as indicated by proportionally long lower segments of the hindlimbs and the presence of an arctometatarsalian pes–a highly modified structure that has been suggested to improve cursorial capability in theropods. Here we describe the osteohistology of the metatarsal II of the holotype of X. zhangi (XMDFEC V 0011). Two rarely reported histological features, radial vascular canals and Sharpey’s fibers, are presented in this study. We suggest that both features are related to the development of the arctometatarsalian pes; however, further investigations of metatarsal osteohistology in theropods are required for the validation of our interpretation.
分类： 生物学 >> 动物学 提交时间： 2019-06-11 合作期刊: 《古脊椎动物学报》
摘要： The late-branching alvarezsaurian Xixianykus zhangi is among the smallest known non-avialan theropods. With great similarity to its close relatives, it is highly cursorial as indicated by proportionally long lower segments of the hindlimbs and the presence of an arctometatarsalian pes–a highly modified structure that has been suggested to improve cursorial capability in theropods. Here we describe the osteohistology of the metatarsal II of the holotype of X. zhangi (XMDFEC V 0011). Two rarely reported histological features, radial vascular canals and Sharpey’s fibers, are presented in this study. We suggest that both features are related to the development of the arctometatarsalian pes; however, further investigations of metatarsal osteohistology in theropods are required for the validation of our interpretation.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The cosmic curvature $\Omega_{K,0}$, which determines the spatial geometry of
the universe, is an important parameter in modern cosmology. Any deviation from
$\Omega_{K,0}=0$ would have a profound impact on primordial inflation paradigm
and fundamental physics. In this work, we adopt a cosmological
model-independent method to test whether $\Omega_{K,0}$ deviates from zero. We
use the Gaussian process to reconstruct the reduced Hubble parameter $E(z)$ and
the derivative of distance $D'(z)$ from observational data, and then determine
$\Omega_{K,0}$ with a null test relation. The cosmic chronometer (CC) Hubble
data, baryon acoustic oscillation (BAO) Hubble data, and supernovae Pantheon
sample are considered. Our result is consistent with a spatially flat universe
within the domain of reconstruction $01$, it tends to favor a closed universe. In this sense, there is
still a possibility for a closed universe. We also carry out the null test of
the cosmic curvature at $0
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The cosmic curvature $\Omega_{K,0}$, which determines the spatial geometry of
the universe, is an important parameter in modern cosmology. Any deviation from
$\Omega_{K,0}=0$ would have a profound impact on primordial inflation paradigm
and fundamental physics. In this work, we adopt a cosmological
model-independent method to test whether $\Omega_{K,0}$ deviates from zero. We
use the Gaussian process to reconstruct the reduced Hubble parameter $E(z)$ and
the derivative of distance $D'(z)$ from observational data, and then determine
$\Omega_{K,0}$ with a null test relation. The cosmic chronometer (CC) Hubble
data, baryon acoustic oscillation (BAO) Hubble data, and supernovae Pantheon
sample are considered. Our result is consistent with a spatially flat universe
within the domain of reconstruction $01$, it tends to favor a closed universe. In this sense, there is
still a possibility for a closed universe. We also carry out the null test of
the cosmic curvature at $0
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the context of the discrepancies between the early and late universe, we emphasize the importance of independent measurements of the cosmic curvature in the late universe. We present an investigation of the model-independent measurement of the cosmic curvature parameter $\Omega_k$ in the late universe with the latest Hubble parameter $H(z)$ measurements and type Ia supernovae (SNe Ia) data. For that, we use two reconstruction methods, the Gaussian process (GP) and artificial neural network (ANN) methods, to achieve the distance construction from $H(z)$ data. In the results obtained by different combinations of observations and reconstruction methods, the tightest constraint on the cosmic curvature is $\Omega_k=-0.03\pm0.11$, in good agreement with zero curvature. This result is the most precise constraint on the cosmic curvature obtained among the recent related estimations. Our findings suggest that the observational data of the late universe support a flat universe.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the context of the discrepancies between the early and late universe, we emphasize the importance of independent measurements of the cosmic curvature in the late universe. We present an investigation of the model-independent measurement of the cosmic curvature parameter $\Omega_k$ in the late universe with the latest Hubble parameter $H(z)$ measurements and type Ia supernovae (SNe Ia) data. For that, we use two reconstruction methods, the Gaussian process (GP) and artificial neural network (ANN) methods, to achieve the distance construction from $H(z)$ data. In the results obtained by different combinations of observations and reconstruction methods, the tightest constraint on the cosmic curvature is $\Omega_k=-0.03\pm0.11$, in good agreement with zero curvature. This result is the most precise constraint on the cosmic curvature obtained among the recent related estimations. Our findings suggest that the observational data of the late universe support a flat universe.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Although general relativity (GR) has been precisely tested at the solar system scale, precise tests at a galactic or cosmological scale are still relatively insufficient. Here, in order to test GR at the galactic scale, we use the newly compiled galaxy-scale strong gravitational lensing (SGL) sample to constrain the parameter $\gamma_{PPN}$ in the parametrized post-Newtonian (PPN) formalism. We employ the Pantheon sample of type Ia supernovae observation to calibrate the distances in the SGL systems using the Gaussian Process method, which avoids the logical problem caused by assuming a cosmological model within GR to determine the distances in the SGL sample. Furthermore, we consider three typical lens models in this work to investigate the influences of the lens mass distributions on the fitting results. We find that the choice of the lens models has a significant impact on the constraints on the PPN parameter $\gamma_{PPN}$. We use the Bayesian information criterion as an evaluation tool to make a comparison for the fitting results of the three lens models, and we find that the most reliable lens model gives the result of $\gamma_{PPN}=1.065^{+0.064}_{-0.074}$, which is in good agreement with the prediction of $\gamma_{PPN}=1$ by GR. As far as we know, our 6.4% constraint result is the best result so far among the recent works using the SGL method.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： With the measurement of the electromagnetic (EM) counterpart, a gravitational wave (GW) event could be treated as a standard siren. As a novel cosmological probe, the standard siren will bring significant implications for cosmology. In this paper, by considering the coincident detections of GW and associated $\gamma$ ray burst (GRB), we find that only about 400 GW bright standard sirens from binary neutron star mergers could be detected in a 10-year observation of the Einstein Telescope and the THESEUS satellite mission. Based on this mock sample, we investigate the implications of GW standard sirens on the interaction between dark energy and dark matter. In our analysis, four viable interacting dark energy (IDE) models, with interaction forms $Q=3\beta H \rho_{\mathrm{de}}$ and $Q=3 \beta H \rho_{\mathrm{c}}$, are considered. Compared with the traditional EM observational data such as CMB, BAO, and SN Ia, the combination of both GW and EM observations could effectively break the degeneracies between different cosmological parameters and provide more stringent cosmological fits. We also find that the GW data could play a more important role for determining the interaction in the models with $Q=3 \beta H \rho_{\mathrm{c}}$, compared with the models with $Q=3\beta H \rho_{\mathrm{de}}$.
分类： 核科学技术 >> 核科学与技术 提交时间： 2023-10-09
摘要： Iron is commonly used as a structural and shielding material in nuclear devices. The accuracy of its nuclear data is critical for the design of nuclear devices. The evaluation data of 56Fe isotopes in the latest version of the CENDL-3.2 library from China was significantly updated. This new data must be tested before it can be used. To test the reliability of this data and assess the shielding effect, a shielding benchmark experiment was conducted with natural Fe spherical samples using a pulsed deuterium- tritium neutron source at the China Institute of Atomic Energy (CIAE). The leakage neutron spectra from the natural spherical iron samples with different thicknesses (4.5, 7.5, and 12 cm) were measured between 0.8-16 MeV after interacting with 14 MeV neutrons using the time-of-flight method. The simulation results were obtained by Monte Carlo simulations by employing the Fe data from the CENDL-3.2, ENDF/B-VIII.0, and JEDNL-5.0 libraries. The measured and simulated leakage neutron spectra and penetration rates were compared, demonstrating that the CENDL-3.2 library performs sufficiently overall. The simulation results of the other two libraries were underestimated for scattering at the continuum energy level.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In recent years, a crisis in the standard cosmology has been caused by inconsistencies in the measurements of some key cosmological parameters, Hubble constant $H_0$ and cosmic curvature parameter $\Omega_K$ for example. It is necessary to remeasure them with the cosmological model-independent methods. In this paper, based on the distance sum rule, we present such a way to constrain $H_0$ and $\Omega_K$ simultaneously in the late universe from strong gravitational lensing time delay (SGLTD) data and gravitational wave (GW) standard siren data simulated from the future observation of the Einstein Telescope (ET). Based on the currently 6 observed SGLTD data, we find that the constraint precision of $H_0$ from the combined 100 GW events can be comparable with the measurement from SH0ES collaboration. As the number of GW events increases to 700, the constraint precision of $H_0$ will exceed that of the \textit{Planck} 2018 results. Considering 1000 GW events as the conservative estimation of ET in ten-year observation, we obtain $H_0=73.69\pm 0.36 \mathrm{~km~s^{-1}~Mpc^{-1}}$ with a 0.5\% uncertainty and $\Omega_K=0.076^{+0.068}_{-0.087}$. In addition, we simulate 55 SGL systems with 6.6\% uncertainty for the measurement of time-delay distance. By combining with 1000 GWs, we infer that $H_0=73.65\pm0.35 \mathrm{~km~s^{-1}~Mpc^{-1}}$ and $\Omega_K=0.008\pm0.048$. Our results suggest that this approach can play an important role in exploring cosmological tensions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Remarkable development of cosmology is benefited from the increasingly improved measurements of cosmic distances including absolute distances and relative distances. In recent years, however, the emerged cosmological tensions motivate us to explore the independent and precise late-universe probes. The two observational effects of strong gravitational lensing (SGL), the velocity dispersions of lens galaxies and the time delays between multiple images, can provide measurements of relative and absolute distances respectively, and their combination is possible to break the degeneracies between cosmological parameters and enable tight constraints on cosmological parameters. In this paper, we combine the observed 130 SGL systems with velocity-dispersion measurements and 7 SGL systems with time-delay measurements to constrain dark-energy cosmological models. It is found that the combination of the two effects does not significantly break the degeneracies between cosmological parameters as expected. However, with the simulations of 8000 SGL systems with well-measured velocity dispersions and 55 SGL systems with well-measured time delays based on the forthcoming LSST survey, we find that the combination of two effects can significantly break the parameter degeneracies, and make the constraint precision of cosmological parameters meet the standard of precision cosmology. We conclude that the observations of SGL will become a useful late-universe probe for precisely measuring cosmological parameters.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Although the cosmic curvature has been tightly constrained in the standard cosmological model using observations of cosmic microwave background anisotropies, it is still of great importance to independently measure this key parameter using only late-universe observations in a cosmological model-independent way. The distance sum rule in strong gravitational lensing (SGL) provides such a way, provided that the three distances in the sum rule can be calibrated by other observations. In this paper, we propose that gravitational waves (GWs) can be used to provide the distance calibration in the SGL method, which can avoid the dependence on distance ladder and cover a wider redshift range. Using the simulated GW standard siren observation by the Einstein Telescope as an example, we show that this scheme is feasible and advantageous. We find that $\Delta\Omega_k\simeq 0.17$ with the current SGL data, which is slightly more precise than the case of using SN to calibrate. Furthermore, we consider the forthcoming LSST survey that is expected to observe many SGL systems, and we find that about $10^4$ SGL data could provide the precise measurement of $\Delta\Omega_k\simeq 10^{-2}$ with the help of GWs. In addition, our results confirm that this method of constraining $\Omega_k$ is strongly dependent on lens models. However, obtaining a more accurate phenomenological model for lens galaxies is highly predictable as future massive surveys observe more and more SGL samples, which will significantly improve the constraint of cosmic curvature.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the near future, the redshift drift observations in optical and radio
bands will provide precise measurements on $H(z)$ covering the redshift ranges
of $2
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： With the measurement of the electromagnetic (EM) counterpart, a gravitational wave (GW) event could be treated as a standard siren. As a novel cosmological probe, the standard siren will bring significant implications for cosmology. In this paper, by considering the coincident detections of GW and associated $\gamma$ ray burst (GRB), we find that only about 400 GW bright standard sirens from binary neutron star mergers could be detected in a 10-year observation of the Einstein Telescope and the THESEUS satellite mission. Based on this mock sample, we investigate the implications of GW standard sirens on the interaction between dark energy and dark matter. In our analysis, four viable interacting dark energy (IDE) models, with interaction forms $Q=3\beta H \rho_{\mathrm{de}}$ and $Q=3 \beta H \rho_{\mathrm{c}}$, are considered. Compared with the traditional EM observational data such as CMB, BAO, and SN Ia, the combination of both GW and EM observations could effectively break the degeneracies between different cosmological parameters and provide more stringent cosmological fits. We also find that the GW data could play a more important role for determining the interaction in the models with $Q=3 \beta H \rho_{\mathrm{c}}$, compared with the models with $Q=3\beta H \rho_{\mathrm{de}}$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Although the cosmic curvature has been tightly constrained in the standard cosmological model using observations of cosmic microwave background anisotropies, it is still of great importance to independently measure this key parameter using only late-universe observations in a cosmological model-independent way. The distance sum rule in strong gravitational lensing (SGL) provides such a way, provided that the three distances in the sum rule can be calibrated by other observations. In this paper, we propose that gravitational waves (GWs) can be used to provide the distance calibration in the SGL method, which can avoid the dependence on distance ladder and cover a wider redshift range. Using the simulated GW standard siren observation by the Einstein Telescope as an example, we show that this scheme is feasible and advantageous. We find that $\Delta\Omega_k\simeq 0.17$ with the current SGL data, which is slightly more precise than the case of using SN to calibrate. Furthermore, we consider the forthcoming LSST survey that is expected to observe many SGL systems, and we find that about $10^4$ SGL data could provide the precise measurement of $\Delta\Omega_k\simeq 10^{-2}$ with the help of GWs. In addition, our results confirm that this method of constraining $\Omega_k$ is strongly dependent on lens models. However, obtaining a more accurate phenomenological model for lens galaxies is highly predictable as future massive surveys observe more and more SGL samples, which will significantly improve the constraint of cosmic curvature.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Strongly lensed type Ia supernovae (SNe Ia) are expected to have some advantages in measuring time delays of multiple images, and so they have a great potential to be developed into a powerful late-universe cosmological probe. In this paper, we simulate a sample of lensed SNe Ia with time-delay measurements in the era of the Legacy Survey of Space and Time (LSST). Based on the distance sum rule, we use lensed SNe Ia to implement model-independent constraints on the Hubble constant $H_0$ and cosmic curvature parameter $\Omega_K$ in the late universe. We find that if 20 lensed SNe Ia could be observed, the constraint on $H_{0}$ is better than the measurement by the SH0ES collaboration. When the event number of lensed SNe Ia increases to 100, the constraint precision of $H_{0}$ is comparable with the result from Planck 2018 data. Considering 200 lensed SNe Ia events as the optimistic estimation, we obtain $\Delta H_0=0.33$ $\rm km\ s^{-1}\ Mpc^{-1}$ and $\Delta\Omega_K=0.053$. In addition, we also simulate lensed quasars in different scenarios to make a comparison and we find that they are still a useful cosmological probe even though the constraint precision from them is much less than that obtained from lensed SNe Ia. In the era of LSST, the measurements of time delay from both lensed SNe Ia and lensed quasars are expected to yield the results of $\Delta H_0=0.26 ~\rm km\ s^{-1}\ Mpc^{-1}$ and $\Delta\Omega_K=0.044$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We forecast constraints on cosmological parameters in the interacting dark energy models using the mock data generated for neutral hydrogen intensity mapping (IM) experiments. In this work, we only consider the interacting dark energy models with energy transfer rate $Q=\beta H\rho_{\rm c}$, and take BINGO, FAST, SKA1-MID, and Tianlai as typical examples of the 21 cm IM experiments. We find that the Tianlai cylinder array will play an important role in constraining the interacting dark energy model. Assuming perfect foreground removal and calibration, and using the Tianlai-alone data, we obtain $\sigma(H_0)=0.19$ km s$^{-1}$ Mpc$^{-1}$, $\sigma(\Omega_{\rm m})=0.0033$ and $\sigma(\sigma_8)=0.0033$ in the I$\Lambda$CDM model, which are much better than the results of Planck+optical BAO (i.e. optical galaxy surveys). However, the Tianlai-alone data cannot provide a very tight constraint on the coupling parameter $\beta$ compared with Planck+optical BAO, while the Planck+Tianlai data can give a rather tight constraint of $\sigma(\beta)=0.00023$ due to the parameter degeneracies being well broken by the data combination. In the I$w$CDM model, we obtain $\sigma(\beta)=0.00079$ and $\sigma(w)=0.013$ from Planck+Tianlai. In addition, we also make a detailed comparison among BINGO, FAST, SKA1-MID, and Tianlai in constraining the interacting dark energy models. We show that future 21 cm IM experiments will provide a useful tool for exploring the nature of dark energy and play a significant role in measuring the coupling between dark energy and dark matter.
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