分类： 力学 >> 力学其他学科 提交时间： 2024-08-13 合作期刊: 《应用力学学报》
摘要： Nb3Sn超导相转变中的力电耦合效应给超导磁体装备的电磁性能指标和安全运行带来不利影响。鉴于Nb3Sn具有立方相和四方相两种相结构,建立了Nb3Sn立方相、四方相和混合相晶体力学模型,以及考虑变形-临界温度退化和变形-正常态电阻率变化的力电耦合响应模型。研究结果表明,相结构会导致单晶体弹性力学性能有所区别,但静水压作用下不同相结构的Nb3Sn多晶体,其局部应力状态与相结构无关,仅取决于晶粒形貌和取向。由于不同的相结构在外载下的费米面上电子态密度的演变规律基本一致,使得变形诱导的临界温度退化行为对相结构没有依赖性。对于混合相Nb3Sn正常态电阻率变化而言,温度低于马氏体相变温度时,可以采用基于电子-电子散射假设得到的T2规律来描述; 当温度高于马氏体相变温度时,由于四方相向立方相的转变,需要考虑电-声子耦合作用对正常态电阻率的贡献,可以采用拓展的Woodard-Cody电阻率模型来描述宏观电阻率的应变效应。研究结果提高了对不同相的临界性能退化机理的认识。
分类： 力学 >> 力学其他学科 提交时间： 2024-08-13 合作期刊: 《应用力学学报》
摘要： 为推动竹结构的发展,展开基于拓扑优化的竹结构设计新方法开发及相应的静力对比试验研究。首先,探讨了运用渐进结构优化指导竹结构设计的系统性方法; 然后结合工程实例,选用面向承压型结构和受拉型结构进化的两种优化可行域,分别开展双车道桥梁结构优化设计并完成静力对比试验。结果表明:基于优化设计的桥梁结构与Michell型桁架结构较吻合,同体积下结构刚度显著高于经验设计构件; 在正常使用状态下,承压型的拓扑拱结构刚度约为受拉型的拓扑悬索结构的3倍,但承载力相较略低。可见,基于渐进结构优化的新设计方法,可以针对不同的承载力和刚度设计要求,构建合适的优化可行域以指导设计出不同的方案,为工程竹结构提供了一种可自动化分析计算的最优化设计方法。
分类： 核科学技术 >> 辐射物理与技术 提交时间： 2024-07-29
摘要： The off-situaccurate reconstruction of the core neutron field is an important step in realizing real-time reactor monitoring. The existing off-situreconstruction method of the neutron field is only applicable to cases wherein a single region changes at a specified location of the core. However, when the neutron field changes are complex, the accurate identification of the individual changed regions becomes challenging, which seriously affects the accuracy and stability of the neutron field reconstruction. Therefore, this study proposed a dual-task hybrid network architecture (DTHNet) for off-situreconstruction of the core neutron field, which trained the outermost assembly reconstruction task and the core reconstruction task jointly such that the former could assist the latter in the reconstruction of the core neutron field under core complex changes. Furthermore, to exploit the characteristics of the ex-core detection signals, this study designed a global-local feature upsamplingmodule that efficiently distributed the ex-core detection signals to each reconstruction unit to improve the accuracy and stability of reconstruction. Reconstruction experiments were performed on the simulation datasets of the CLEAR-I reactor to verify the accuracy and stability of the proposed method. The results showed that when the location uncertainty of a single region did not exceed nine and the number of multiple changed regions did not exceed five. Further, the reconstructed ARD was within 2%, RDmaxwas maintained within 17.5%, and the number of RD≥10% was maintained within 10. Furthermore, when the noise interference of the ex-core detection signals were within ±2%, although the average number of RD≥10%increased to 16, the average ARD was still within in 2%, and the average RDmaxwas within 22%. Collectively, these results show that, theoretically, the DTHNetcan accurately and stably reconstruct most of the neutron field under certain complex core changes.
分类： 核科学技术 >> 核科学技术其他学科 提交时间： 2024-02-01
摘要： Betavoltaic nuclear batteries show promise as compact and enduring power sources for microelectromechanical systems (MEMS). Current theoretical calculations often overlook practical diode characteristics like surface recombination (S), bulk recombination within the space-charge region (R-SCR), series resistance (Rs) and shunt resistance (Rsh), resulting in significant gaps between theoretical predictions and experimental results, with differences in JSC, VOC, or converter efficiency up to tenfold. To address this, a Practical Diode Model, integrating these practical characteristics, is developed via Monte Carlo and Physics-Based Compact Model Co-Simulation.We quantitatively analyze the differential impacts and synergistic effects of these practical characteristics on JSC, VOC, FF, and Pout, highlighting the detrimental effects of S, R-SCR, and Rs, while emphasizing the beneficial role of Rsh. Further analysis of the degree of influence of S, Rs, and Rsh on output power reveals a priority ranking order of Rs, S, and Rsh for Si-based batteries, and S, Rsh, and Rs for SiC-based batteries. This approach effectively bridges the theoretical-experimental gap, evidenced by J-V curves closely matching tested batteries and negligible relative errors of -0.8% to 0.6% between Pout values and their tested counterparts, emphasizing its accuracy in predictions. We predict output performance across material qualities, obtaining achievable powers of 16.82 and 73.90 nW/cm2 for planar Si- and SiC-based batteries, and evaluate the quality levels of existing batteries. Furthermore, our model can forecast the performance of 3D batteries by incorporating an extended electron-hole pair generation rate model into 3D structures, achieving 28 W/cm3 for the 63Ni-Si-based multi-layer battery, surpassing planar silicon and suitable for MEMS applications.
分类： 医学、药学 >> 预防医学与公共卫生学 提交时间： 2024-08-13
摘要： 背景 类风湿因子（RF）是原发性干燥综合征（pSS）患者中常见的自身抗体，其在疾病中的具体作用尚不完全清楚。目的 探索不同水平RF在 pSS中的临床特点及意义。方法 采用调查研究的方法，纳入2018年12月—2022年9月于中日友好医院中医风湿病科就诊的 262 例 pSS 患者为研究对象。依据 RF 水平将患者分为3组：阴性组137例（RF60 U/mL）。采集 3 组pSS 患者的临床资料，包括一般资料、临床表现、症状评分、血液学指标，采用 χ2 、非参数及趋势检验分析组间差异。结果 262 例 pSS 患者 RF 阳性率为 47.7%（125/262），其中男 14 例（5.3%）、女 248 例（94.7%），中位年龄 57.0（49.0，63.0）岁，平均发病年龄（48.7±11.6）岁，中位病程 60.0（24.0，120.0）个月；3 组 pSS 患者性别、年龄、发病年龄、病程比较，差异均无统计学意义（P>0.05）。pSS 患者常见临床表现前 3 位的依次为：口干 257 例、眼干 247 例、乏力 235 例；高滴度阳性组血液系统受累、关节炎发生率高于阴性组（P<0.05）；随着 RF 滴度的增加，pSS 患者血液系统受累（χ2 趋势 =6.992，P 趋势 =0.008）、关节炎（χ2 趋势 =10.918，P 趋势 =0.001）发生率呈上升趋势。随着 RF 滴度的增加，pSS 患者抗核抗体≥ 1 ∶ 160（χ2 趋势 =40.691，P 趋势 <0.001）、抗干燥综合征相关抗原 A 抗体阳性（χ2 趋势 =26.138，P 趋势 <0.001）、抗 Ro52 核糖核蛋白抗体阳性（χ2 趋势 =31.426，P 趋势 <0.001）、抗干燥综合征相关抗原 B 抗体阳性（χ2趋势 =23.682，P 趋势 <0.001）、红细胞沉降率升高（χ2 趋势 =40.132，P 趋势 <0.001）、免疫球蛋白（Ig）A 升高（χ2 趋势 =7.508，P 趋势 =0.006）、IgG 升高（χ2 趋势 =71.570，P 趋势 <0.001）、补体 3 降低（χ2 趋势 =7.452，P 趋势 =0.006）、中性粒细胞计数降低（χ2 趋势 =8.364，P 趋势 =0.004）、血红蛋白降低（χ2 趋势 =6.390，P 趋势 =0.011）的比例呈上升趋势。结论 随着RF 滴度升高，pSS 患者血清免疫异常、腺体外受累的比例增加；RF 滴度升高对关节炎、血液系统受累具有预测价值。
分类： 医学、药学 >> 预防医学与公共卫生学 提交时间： 2024-08-13
摘要： 背景 骨关节疾病是老年人群常见、多发的慢性疾病，其与更高的死亡率、更多的残疾、功能状态的下降和较低的生命质量显著相关，产生巨大的疾病负担。目前尚无河南省该病流行情况及其影响因素的研究。目的 了解河南省老年人群骨关节疾病流行特征及其影响因素，为其实施精准防控提供科学依据。方法 采用多阶段随机整群抽样方法，通过调查问卷、医学体检、实验室检测等方法，获取 2018 年河南省≥ 18 岁常住居民人口学特征、既往疾病史、身体活动及身体指标等，本研究纳入 1 055 名≥ 60 岁人为研究对象。运用基于复杂抽样构建的多因素Logistic 回归分析河南省不同特征老年人群骨关节疾病特征及其影响因素。结果 2018 年河南省老年人群骨关节疾病患病率（加权后）为 28.13%（95%CI=28.10%~28.15%）。其中女性、城市、超重或肥胖、中心性肥胖、血脂异常或高脂血症、无吸烟史、有打鼾史、中等强度活动的老年人群骨关节疾病患病率更高，差异均有统计学意义（P<0.05）。多因素 Logistic 回归分析显示，男性（OR=0.717，95%CI=0.550~0.933，P=0.013）是老年人群骨关节疾病的保护因素；超重或肥胖（OR=1.329，95%CI=1.050~1.684，P=0.018）、中心性肥胖（OR=1.305，95%CI=1.047~1.626，P=0.018）是老年人群骨关节疾病的危险因素。结论 河南省老年人群骨关节疾病与性别、BMI 和中心性肥胖相关，应对老年人群中女性、超重或肥胖和中心性肥胖者开展针对性健康教育及综合干预。
分类： 核科学技术 >> 辐射物理与技术 提交时间： 2024-07-29
Can Cheng
Yong-Ji Xie
Xun-Rong Xia
Jia-Yu Gu
Dong Zhao
Yi-Ze Chen
Ai-Yun Sun
Xu-Wen Liang
Wen-Bao Jia
Da-Qian Hei
摘要： Neutron-induced gamma-ray imaging is a spectroscopic technique that uses characteristic gamma rays to infer the elemental distribution of an object. Currently, this technique requires the use of large facilities to supply a high neutron flux and a time-consuming detection procedure involving direct collimating measurements. In this study, a new method based on low neutron flux was proposed. A single-pixel gamma ray detector combined with random pattern gamma ray masks was used to measure the characteristic gamma rays emitted from the sample. Images of the elemental distribution in the sample, comprising 30 × 30 pixels, were reconstructed using the maximum-likelihood expectation-maximization algorithm. The results demonstrate that the elemental imaging of the sample can be accurately determined using this method. The proposed approach, which eliminates the need for high neutron flux and scanning measurements, can be used for in-field imaging applications.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Solar System's orbital structure is thought to have been sculpted by an episode of dynamical instability among the giant planets. However, the instability trigger and timing have not been clearly established. Hydrodynamical modeling has shown that while the Sun's gaseous protoplanetary disk was present the giant planets migrated into a compact orbital configuration in a chain of resonances. Here we use dynamical simulations to show that the giant planets' instability was likely triggered by the dispersal of the gaseous disk. As the disk evaporated from the inside-out, its inner edge swept successively across and dynamically perturbed each planet's orbit in turn. The associated orbital shift caused a dynamical compression of the exterior part of the system, ultimately triggering instability. The final orbits of our simulated systems match those of the Solar System for a viable range of astrophysical parameters. The giant planet instability therefore took place as the gaseous disk dissipated, constrained by astronomical observations to be a few to ten million years after the birth of the Solar System. Terrestrial planet formation would not complete until after such an early giant planet instability; the growing terrestrial planets may even have been sculpted by its perturbations, explaining the small mass of Mars relative to Earth.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Building accurate and predictive models of the underlying mechanisms of celestial motion has inspired fundamental developments in theoretical physics. Candidate theories seek to explain observations and predict future positions of planets, stars, and other astronomical bodies as faithfully as possible. We use a data-driven learning approach, extending that developed in Lu et al. ($2019$) and extended in Zhong et al. ($2020$), to a derive stable and accurate model for the motion of celestial bodies in our Solar System. Our model is based on a collective dynamics framework, and is learned from the NASA Jet Propulsion Lab's development ephemerides. By modeling the major astronomical bodies in the Solar System as pairwise interacting agents, our learned model generate extremely accurate dynamics that preserve not only intrinsic geometric properties of the orbits, but also highly sensitive features of the dynamics, such as perihelion precession rates. Our learned model can provide a unified explanation to the observation data, especially in terms of reproducing the perihelion precession of Mars, Mercury, and the Moon. Moreover, Our model outperforms Newton's Law of Universal Gravitation in all cases and performs similarly to, and exceeds on the Moon, the Einstein-Infeld-Hoffman equations derived from Einstein's theory of general relativity.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Presolar grains are microscopic dust grains that formed in the stellar winds or explosions of ancient stars that died before the formation of the solar system. The majority (~90% in number) of presolar silicon carbide (SiC) grains, including types mainstream (MS), Y, and Z, came from low-mass C-rich asymptotic giant branch (AGB) stars, which is supported by the ubiquitous presence of SiC dust observed in the circumstellar envelope of AGB stars and the signatures of slow neutron-capture process preserved in these grains. Here, we review the status of isotope studies of presolar AGB SiC grains with an emphasis on heavy-element isotopes and highlight the importance of presolar grain studies for nuclear astrophysics. We discuss the sensitives of different types of nuclei to varying AGB stellar parameters and how their abundances in presolar AGB SiC grains can be used to provide independent, detailed constraints on stellar parameters, including 13C formation, stellar temperature, and nuclear reaction rates.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The exchange of a pair of neutrinos between two objects, seperated by a distance $r$, leads to a long-range effective potential proportional to $1/r_{}^5$, assuming massless neutrinos and four-fermion contact interactions. In this paper, we investigate how this known form of neutrino-mediated potentials might be altered if the distance $r$ is sufficiently short, corresponding to a sufficiently large momentum transfer which could invalidate the contact interactions. We consider two possible scenarios to open up the contact interactions by introducing a $t$-channel or an $s$-channel mediator. We derive a general formula that is valid to describe the potential in all regimes as long as the external particles remain non-relativistic. In both scenarios, the potential decreases as $1/r_{}^5$ in the long-range limit as expected. In the short-range limit, the $t$-channel potential exhibits the Coulomb-like behavior (i.e. proportional to $1/r$), while the $s$-channel potential exhibits $1/r_{}^4$ and $1/r_{}^2$ behaviors.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Inverse mass cascade is a key feature of statistically steady state for self-gravitating collisionless dark matter flow (SG-CFD). Continuous mass transfer from small to large mass scales (inverse) is formulated. Direct effect of mass cascade on halo mass function is presented. Mass cascade is local, two-way, and asymmetric in mass space. Halos inherit/pass their mass from/to halos of similar size. Two regimes are identified: a propagation range with scale-independent rate of mass transfer and a deposition range with cascaded mass consumed to grow halos. Dimensional analysis leads to a power-law mass function in propagation range with a geometry exponent ${\lambda}$. A fundamental merging frequency $f_0{\sim}m_p^{\lambda-1}a^{-1}$ is identified, where $a$ is scale factor. Particle mass $m_p$ can be determined if that frequency is known. Rate of mass transfer ${\epsilon}_m{\sim}a^{-1}$ is independent of halo mass, a key feature of propagation range. Typical halos grow as $m_h{\sim}a^{3/2}$ and halo lifespan scales as ${\sim}m_h^{-\lambda}$. Chain reaction of mass cascade provides non-equilibrium dark matter flow a mechanism to continuously release energy and maximize entropy. Continuous injection of mass ("free radicals") at the smallest scale is required to sustain the everlasting inverse mass cascade such that total halo mass $M_h$ increases as $a^{1/2}$. These "radicals" might be directly generated at the smallest Planck scale or by a direct cascade from large to small scales. Entire mass cascade can be formulated by random walk in mass space, where halos migrate with an exponential distribution of waiting time. This results in a heterogeneous diffusion model, where Press-Schechter mass function can be fully derived without relying on any specific collapse models. A double-$\lambda$ mass function is proposed with different $\lambda$ for two ranges and agrees with N-body simulations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Measuring the Cosmic X-ray Background (CXB) is a key to understand the Active Galactic Nuclei population, their absorption distribution and their average spectra. However, hard X-ray instruments suffer from time-dependent backgrounds and cross-calibration issues. The uncertainty of the CXB normalization remain of the order of 20%. To obtain a more accurate measurement, the Monitor Vsego Neba (MVN) instrument was built in Russia but not yet launched to the ISS (arXiv:1410.3284). We follow the same ideas to develop a CXB detector made of four collimated spectrometers with a rotating obturator on top. The collimators block off-axis photons below 100 keV and the obturator modulates on-axis photons allowing to separate the CXB from the instrumental background. Our spectrometers are made of 20 mm thick CeBr$_{3}$ crystals on top of a SiPM array. One tube features a $\sim$20 cm$^2$ effective area and more energy coverage than MVN, leading to a CXB count rate improved by a factor of $\sim$10 and a statistical uncertainty $\sim$0.5% on the CXB flux. A prototype is being built and we are seeking for a launch opportunity.
分类： 物理学 >> 核物理学 分类： 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间： 2024-08-09
摘要： Scanning magnets are devices responsible for deflecting particles to specific locations in particle therapy utilizing spot scanning techniques. To ensure the distortion of the scanned beams’ shapes remains within an acceptable level, it is necessary to guarantee that the homogeneity of the field integrals is sufficiently high in the two transversal directions within the good field region. Typically, this is accomplished by adding shims on both sides of magnet poles. In this study, we innovatively proposed a method to perform multi-objective optimization of shim parameters and excitation currents by the state-of-the-art evolutionary algorithm Non- dominated Sorting Genetic Algorithm-III (NSGA-III). Furthermore computer vision (CV) was implemented to automatically evaluate both the beam shape distortions and the centroids of the scanned beam spots at the target plane to assist efficient optimization process. With this method, optimal parameters of scanning magnets which have capability of scanning a carbon beam of 400 MeV/u beam energy across a 20 cm × 20 cm field size with a source-to-axis distance of 255 cm were obtained successfully. Meanwhile, we also conducted eddy current and temperature rise analysis, laminated steel plates with 19 slits cut near the pole gaps were used to reduce eddycurrents due to rapid variation of magnetic fields during the scanning process. Based on the optimized magnetsparameters, eddy current and temperature analyses were performed and the temperature rises were found to be near 40°C and 54°C for the Y and X magnets respectively at the designed scanning speeds, which meets the requirements for normal operation. This proposed procedure of optimization is expected to facilitate efficient and sophisticated design of various magnets applied to charged particle accelerators.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Salvatore Ferrone
Paola Di Matteo
Alessandra Mastrobuono-Battisti
Misha Haywood
Owain N. Snaith
Marco Montouri
Sergey Khoperskov
David Valls-Gabaud
摘要： We present the e-TidalGCs Project which aims at modeling and predicting the extra-tidal features surrounding all Galactic globular clusters for which 6D phase space information, masses and sizes are available (currently 159 globular clusters). We focus the analysis and presentation of the results on the distribution of extra-tidal material on the sky, and on the different structures found at different heliocentric distances. We emphasize the wide variety of morphologies found: beyond the canonical tidal tails, our models reveal that the extra-tidal features generated by globular clusters take a wide variety of shapes, from thin and elongated shapes, to thick, and complex halo-like structures. We also compare some of the most well studied stellar streams found around Galactic globular clusters to our model predictions, namely those associated to the clusters NGC 3201, NGC 4590, NGC 5466 and Pal 5. Additionally, we investigate how the distribution and extension in the sky of the simulated streams vary with the Galactic potential by making use of three different models, containing or not a central spheroid, or a stellar bar. Overall, our models predict that the mass lost by the current globular cluster population in the field from the last 5 Gyrs is between $0.3-2.1\times10^{7}M_{\odot}$, an amount comparable between 7-55 % of current mass. Most of this lost mass is found in the inner Galaxy, with the half-mass radius of this population being between 4-6 kpc. The outputs of the simulations will be publicly available, at a time when the ESA Gaia mission and complementary spectroscopic surveys are delivering exquisite data to which these models can be compared.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Dark radiation (DR) is generally predicted in new physics scenarios that address fundamental puzzles of the Standard Model or tensions in the cosmological data. Cosmological data has the sensitivity to constrain not only the energy density of DR, but also whether it is interacting. In this paper, we present a systematic study of five types of interacting DR (free-streaming, fluid, decoupling, instantaneous decoupling, and recoupling DR) and their impact on cosmological observables. We modify the Boltzmann hierarchy to describe all these types of interacting DR under the relaxation time approximation. We, for the first time, robustly calculate the collision terms for recoupling scalar DR and provide a better estimation of the recoupling transition redshift. We demonstrate the distinct features of each type of DR on the CMB and matter power spectra. We perform MCMC scans using the Planck 2018 data and BAO data. Assuming no new physics in the SM neutrino sector, we find no statistically significant constraints on the couplings of DR, although there is a slight preference for a late transition redshift for instantaneous decoupling DR around recombination, and for the fluid-like limit of all the cases. The $\Delta N_{\rm eff}$ constraint varies marginally depending on the type of DR.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Compact Obscured Nuclei (CONs) account for a significant fraction of the population of luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs). These galaxy nuclei are compact, with radii of 10-100~pc, with large optical depths at submm and far-infrared wavelengths, and characterized by vibrationally excited HCN emission. It is not known what powers the large luminosities of the CON host galaxies because of the extreme optical depths towards their nuclei. CONs represent an extreme phase of nuclear growth, hiding either a rapidly accreting supermassive black hole or an abnormal mode of star formation. Here we apply principal component analysis (PCA) tomography to high-resolution (0.06$^{\prime\prime}$) ALMA observations at frequencies 245 to 265~GHz of the nearby CON (59~Mpc) IC~860. PCA is a technique to unveil correlation in the data parameter space, and we apply it to explore the morphological and chemical properties of species in our dataset. The leading principal components reveal morphological features in molecular emission that suggest a rotating, infalling disk or envelope, and an outflow analogous to those seen in Galactic protostars. One particular molecule of astrochemical interest is methanimine (CH$_2$NH), a precursor to glycine, three transitions of which have been detected towards IC 860. We estimate the average CH$_2$NH column density towards the nucleus of IC~860 to be $\sim10^{17}$cm$^{-2}$, with an abundance exceeding $10^{-8}$ relative to molecular hydrogen, using the rotation diagram method and non-LTE radiative transfer models. This CH$_2$NH abundance is consistent with those found in hot cores of molecular clouds in the Milky Way. Our analysis suggests that CONs are an important stage of chemical evolution in galaxies, that are chemically and morphologically similar to Milky Way hot cores.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Christopher J. White
Patrick D. Mullen
Yan-Fei Jiang
Shane W. Davis
James M. Stone
Viktoriya Morozova
Lizhong Zhang
摘要： We extend the general-relativistic magnetohydrodynamics (GRMHD) capabilities of Athena++ to incorporate radiation. The intensity field in each finite-volume cell is discretized in angle, with explicit transport in both space and angle properly accounting for the effects of gravity on null geodesics, and with matter and radiation coupled in a locally implicit fashion. Here we describe the numerical procedure in detail, verifying its correctness with a suite of tests. Motivated in particular by black hole accretion in the high-accretion-rate, thin-disk regime, we demonstrate the application of the method to this problem. With excellent scaling on flagship computing clusters, the port of the algorithm to the GPU-enabled AthenaK code now allows the simulation of many previously intractable radiation-GRMHD systems.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Supernova (SN) cosmology is based on the assumption that the width-luminosity relation (WLR) and the color-luminosity relation (CLR) in the type Ia SN luminosity standardization would not show {absolute magnitude differences} with progenitor age. Unlike this expectation, recent age datings of stellar populations in host galaxies have shown significant correlations between progenitor age and Hubble residual (HR). Here we show that this correlation originates from a strong progenitor age dependence of the zero-points of the WLR and the CLR, in the sense that SNe from younger progenitors are fainter each at given light-curve parameters $x_1$ and $c$. This $4.6\sigma$ result is reminiscent of Baade's discovery of the zero-point variation of the Cepheid period-luminosity relation with age, and, as such, causes a serious systematic bias with redshift in SN cosmology. Other host properties show substantially smaller and insignificant offsets in the WLR and CLR for the same dataset. We illustrate that the differences between the high-$z$ and low-$z$ SNe in the WLR and CLR, and in HR after the standardization, are fully comparable to those between the correspondingly young and old SNe at intermediate redshift, indicating that the observed dimming of SNe with redshift may well be an artifact of over-correction in the luminosity standardization. When this systematic bias with redshift is properly taken into account, there is little evidence left for an accelerating universe, in discordance with other probes, urging the follow-up investigations with larger samples at different redshift bins.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We develop a framework for using clustering-based redshift inference (cluster-$z$) to measure the evolving galaxy luminosity function (GLF) and galaxy stellar mass function (GSMF) using WISE W1 ($3.4\mu m$) mid-infrared photometry and positions. We use multiple reference sets from the Galaxy And Mass Assembly (GAMA) survey, Sloan Digital Sky Survey (SDSS) and Baryon Oscillation Spectroscopic Survey (BOSS). Combining the resulting cluster-$z$s allows us to enlarge the study area, and by accounting for the specific properties of each reference set, making best use of each reference set to produce the best overall result. Thus we are able to measure the GLF and GSMF over $\sim 7500\, \mathrm{deg}^2 $ of the Northern Galactic Cap (NGC) up to $z<0.6$. Our method can easily be adapted for new studies with fainter magnitudes, which pose difficulties for the derivation of photo-$z$s. The measurement of the GSMF is currently limited by the models for k-corrections and mass-to-light ratios, rather than more complicated effects tied to the evolution of the differential galaxy bias. With better statistics in future surveys this technique is a strong candidate for studies with new emerging data from, e.g. the Vera C. Rubin Observatory, the Euclid mission or the Nancy Grace Roman Space Telescope.
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