分类： 生物学 >> 动物学 提交时间： 2021-07-30 合作期刊: 《古脊椎动物学报》
摘要： 乳齿象类是长鼻类演化的重要阶段，该阶段奠定了长鼻类各冠群演化的基本格局。乳齿象类的研究有400多年的历史，分类和命名经过多次修订改动，乳齿象类的演化脉络完全体现在乳齿象命名历史之中。从词源学角度考证乳齿象类各类群的命名来源，整理了175条乳齿象类的中文译名(绝大多数为有效分类名), 包括12个属以上分类群，46个属，117个种，涵盖了乳齿象类几乎全部的种属。在此基础上梳理了乳齿象类的演化脉络，提出乳齿象类分类和命名中存在的一些问题。乳齿象类的头骨和下颌的演化在各支系中都是连续的，体现出了相近的平行演化趋势，而颊齿的形态特征虽然区别不明显，但在各支系中相对稳定。豕棱齿象科(Choerolophodontidae)是乳齿象类中最稳健的单系群，其中厚棱象(Synconolophus)可能是有效属名；玛姆象科中，中新乳齿象(Miomastodon)和上新乳齿象(Pliomastodon)可能都是有效的，但不一定是美洲乳齿象(Mammut americanum)的直接祖先；铲齿象科(Amebelodontidae)中达氏铲齿象(Platybelodon danovi)与格氏铲齿象(P. grangeri)、赵氏隐门齿象(Aphanobelodon zhaoi)的系统发育关系存在疑问，取决于P.danovi的下门齿断面究竟是否为齿柱状结构，而美洲的布氏柱门齿象(Konobelodon britti) 可能是卢氏匙门齿象(Torynobelodon loomisi)的同物异名，亚洲归入Konobelodon的种不一定是铲齿象类，可能应归为副四棱齿象(Paratetralophodon); 嵌齿象科(Gomphotheriidae)中锯齿象属(Serridentinus)可能有效，它代表了嵌齿象类中一个偏轭型化的类群，向居维叶象亚科方向演化；居维叶象亚科(Cuvieroniinae)可能仅包括居维叶象(Cuvieronius)和喙嘴象(Rhynchotherium)属，而美洲其他的短颌嵌齿象类中，脊乳齿象(Stegomastodon)有可能从铲 齿象科中的一支演化而来，南方乳齿象(Notiomastodon)则可能与中华乳齿象(Sinomastodon)相关；Sinomastodon可能起源于中国南方的竹棚上新乳齿象(Pliomastodon (?) zhupengensis),原来的属型种中间中华乳齿象(Sinomastodon intermedius)具有早出原同名，建议以它的早出异名仙台中华乳齿象(Sinomastodon sendaicus)取代S. intermedius。
分类： 生物学 >> 动物学 提交时间： 2020-03-31 合作期刊: 《古脊椎动物学报》
摘要： The elephantimorph proboscideans, Serridentinus gobiensis Osborn & Granger, 1932, and Miomastodon tongxinensis Chen, 1978, from the Middle Miocene of northern China, were revised as Zygolophodon gobiensis (Osborn & Granger, 1932). However, their phylogenetic positions are still being debated because of their intermediate morphology between the typical bunodont (Gomphotheriidae) and zygodont (Mammutidae) elephantimorphs. In the present paper, we compare their dental and mandibular morphology with that of the Eurasian Z. turicensis, Gomphotherium subtapiroideum, and G. tassyi, as well as the North American Mio. merriami and G. productum. It appears that S. gobiensis and Mio. tongxinensis share with Mio. merriami the slightly more bunodont molar morphology than that of Z. turicensis, e.g., the thicker enamel, thicker pretrite crescentoids, higher interlophid enamel pillars in buccal view, and the narrower contour majorly caused by the narrower posttrite half loph(id)s. S. gobiensis and Mio. merriami also possess an “erected oval cross-sectioned mandibular tusk”, in which the cross-section is mediolaterally compressed (dorsoventral diameter being larger than the mediolateral one). Whereas, in Z. turicensis and G. productum, the mandibular tusk is “laid oval cross-sectioned”, in which the cross-section is dorsoventrally compressed (dorsoventral diameter is smaller than the mediolateral one). Therefore, it is reasonable to revive the genus Miomastodon Osborn, 1922, which contains the species that were previously attributed to Zygolophodon, but they have relatively bunodont molar morphology (i.e., the robust type of the Z. turicensis group). The mandibular tusk with erected oval cross-section seems to be a synapomorphy of Miomastodon species. Furthermore, the molar morphology of G. subtapiroideum and G. tassyi also exhibits intermediate status between the typical bunodonts and zygodonts. However, the mandibular symphysis of G. subtapiroideum and G. tassyi is stronger than that of Miomastodon, and the mandibular tusk is pyriform cross-sectioned. The validity of Miomastodon and G. subtapiroideum/tassyi obscures the boundary between the Gomphotheriidae and Mammutidae, and suggests that the evolutions of the Gomphotheriidae and Mammutidae are deeply involved in with each other, rather than straightforwardly detached. This phenomenon has been revealed by a collagen sequence analysis among Notiomastodon, Mammut, and extant elephants, which should be further studied.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： We clarify theoretically that the topological ring-cavity (TRC) modes propagating along the interface between two honeycomb-type photonic crystals distinct in topology can be exploited for achieving stable single-mode lasing, with the maximal intensity larger than a whispering-gallery-mode counterpart by order of magnitude. Especially, we show that the TRC modes located at the bulk bandgap center benefit maximally from the gain profile since they are most concentrated and uniform along the ring cavity, and that, inheriting from the Dirac-like dispersion of topological interface states, they are separated in frequency from each other and from other photonic modes, both favoring intrinsically single-mode lasing. A TRC mode running in a specific direction with desired orbital angular momentum can be stimulated selectively by injecting circularly polarized light. The TRC laser proposed in the present work can be fabricated by means of advanced semiconductor nanotechnologies, which generates chiral laser beams ideal for novel photonic functions.
分类： 生物学 >> 动物学 提交时间： 2021-08-11 合作期刊: 《古脊椎动物学报》
摘要： A cuboid specimen collected from the Late Miocene stratum at Qingyang, Gansu, China is described here. The size of the Qingyang specimen is comparatively huge, even larger than the average size of Elasmotherium caucasicum collected from Nihewan, Hebei, China. The morphology of the Qingyang specimen is identical to that of other specimens of Elasmotheriini; thus, the Qingyang specimen belongs to a huge elasmothere, most probably Sinotherium. By comparison with extant rhino species, the complex of the main body and the apophysis exhibit functional significance. The angle between the frontal plate of the cuboid and the main axis of the apophysis can suggest the ecological conditions occupied by an elasmothere. From analysis of the morphology of the cuboid, Sinotherium and the more derived elasmotheres probably lived in forested or wooded environments, differing from the previous hypothesis of their paleoenvironment.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： A crucial subroutine for various quantum computing and communication algorithms is to efficiently extract different classical properties of quantum states. In a notable recent theoretical work by Huang, Kueng, and Preskill [Nat. Phys. 16, 1050 (2020)], a thrifty scheme showed how to project the quantum state into classical shadows and simultaneously predict $M$ different functions of a state with only $\mathcal{O}(\log_2 M)$ measurements, independent of the system size and saturating the information-theoretical limit. Here, we experimentally explore the feasibility of the scheme in the realistic scenario with a finite number of measurements and noisy operations. We prepare a four-qubit GHZ state and show how to estimate expectation values of multiple observables and Hamiltonians. We compare the measurement strategies with uniform, biased, and derandomized classical shadows to conventional ones that sequentially measure each state function exploiting either importance sampling or observable grouping. We next demonstrate the estimation of nonlinear functions using classical shadows and analyze the entanglement of the prepared quantum state. Our experiment verifies the efficacy of exploiting (derandomized) classical shadows and sheds light on efficient quantum computing with noisy intermediate-scale quantum hardware.
分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2017-03-26
摘要： Two cryogenic systems of high purity germanium detector, liquid nitrogen and mechanical coolers, are expound, together with explanations of merits and demerits for each kind of cooling methods. The resolutions of detector to the characteristic lines of 152Eu under different cooling conditions are studied. The laboratory results indicate that the mechanical cooler (X-Cooler II) is an ideal replacement candidate for the liquid nitrogen cooler that is being utilized by BEMS at BEPC-II.
分类： 物理学 >> 基本粒子与场物理学 分类： 物理学 >> 凝聚态:电子结构、电、磁和光学性质 分类： 电子与通信技术 >> 电子技术 分类： 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间： 2025-03-29
摘要： The self-force and the self-energy (Coulomb-velocity energy) of an electron moving along a rectilinear trajectory in the vacuum is analyzed numerically. It is illustrated for the first time that when the velocity of the electron approaches the light velocity in the vacuum, the Coulomb-velocity energy approaches infinitely large, so is the self-force. Consequently, electrons cannot be accelerated to move faster than the light in the vacuum using electric accelerators because infinite large external force may be required to make the electron cross the electromagnetic barrier of the light velocity in the vacuum. Based on the observation, the Bertozzi experiment is re-interpreted, which shows that the velocity limit is due to the intrinsic behavior of the electron that can be clearly explained with the classical Maxwell’s theory. It is obviously not so definite that this behavior of the electron is due to the effect of special relativity as claimed in text books. Therefore, the outcome of the Bertozzi experiment may be not an unquestionable experimental support to the Einstein’s theory of special relativity. It is natural to consider that neutral particles may move faster than the light velocity in the vacuum because they do not face the big electromagnetic self-force when they cross the electromagnetic barrier. Furthermore, a reasonable hypothesis can be made that superluminal electrons may be generated by the collision of high energy particles in a collider or in the universe.
分类： 地球科学 >> 大气科学 提交时间： 2024-06-21 合作期刊: 《干旱区科学》
摘要： Stable water isotopes are natural tracers quantifying the contribution of moisture recycling to local precipitation, i.e., the moisture recycling ratio, but various isotope-based models usually lead to different results, which affects the accuracy of local moisture recycling. In this study, a total of 18 stations from four typical areas in China were selected to compare the performance of isotope-based linear and Bayesian mixing models and to determine local moisture recycling ratio. Among the three vapor sources including advection, transpiration, and surface evaporation, the advection vapor usually played a dominant role, and the contribution of surface evaporation was less than that of transpiration. When the abnormal values were ignored, the arithmetic averages of differences between isotope-based linear and the Bayesian mixing models were 0.9% for transpiration, 0.2% for surface evaporation, and –1.1% for advection, respectively, and the medians were 0.5%, 0.2%, and –0.8%, respectively. The importance of transpiration was slightly less for most cases when the Bayesian mixing model was applied, and the contribution of advection was relatively larger. The Bayesian mixing model was found to perform better in determining an efficient solution since linear model sometimes resulted in negative contribution ratios. Sensitivity test with two isotope scenarios indicated that the Bayesian model had a relatively low sensitivity to the changes in isotope input, and it was important to accurately estimate the isotopes in precipitation vapor. Generally, the Bayesian mixing model should be recommended instead of a linear model. The findings are useful for understanding the performance of isotope-based linear and Bayesian mixing models under various climate backgrounds.
分类： 信息科学与系统科学 >> 信息科学与系统科学基础学科 分类： 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 分类： 天文学 >> 天文学 提交时间： 2024-05-22
摘要： The electromagnetic fields of point sources with time varying charges moving in the vacuum are derived using the Liénard-Wiechert potentials. The properties of the propagation velocities and the Doppler effect are discussed based on their far fields. The results show that the velocity of the electromagnetic waves and the velocity of the sources cannot be added like vectors; the velocity of electromagnetic waves of moving sources are anisotropic in the vacuum; the transverse Doppler shift is intrinsically included in the fields of the moving sources and is not a pure relativity effect caused by time dilation. Since the fields are rigorous solutions of the Maxwell’s equations, the findings can help us to abort the long-standing misinterpretations concerning about the classic mechanics and the classic electromagnetic theory. Although it may violate the theory of the special relativity, we show mathematically that, when the sources move faster than the light in the vacuum, the electromagnetic barriers and the electromagnetic shock waves can be clearly predicted using the exact solutions. Since they cannot be detected by observers in the region outside their shock wave zones, an intuitive and reasonable hypothesis can be made that the superluminal sources may be considered as a kind of electromagnetic blackholes.
分类： 信息科学与系统科学 >> 信息科学与系统科学基础学科 分类： 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 分类： 电子与通信技术 >> 光电子学与激光技术 分类： 物理学 >> 地球物理学、天文学和天体物理学 分类： 物理学 >> 基本粒子与场物理学 提交时间： 2024-04-08
摘要： The Einstein’s theory of special relativity is based on his two postulates. The first is that the laws of physics are the same in all inertial reference frames. The second is that the velocity of light in the vacuum is the same in all inertial frames. The theory of special relativity is considered to be supported by a large number of experiments. This paper revisits the two postulates according to the new interpretations to the exact solutions of moving sources in the laboratory frame. The exact solutions are obtained using the classic Maxwell’s theory, which clearly show that the propagation velocity of the electromagnetic waves of moving sources in the vacuum is not isotropic; the propagation velocity of the electromagnetic waves and the moving velocity of the sources cannot be added like vectors; the transverse Doppler effect is intrinsically included in the fields of the moving sources. The electromagnetic sources are subject to the Newtonian mechanics, while the electromagnetic fields are subject to the Maxwell’s theory. We argue that since their behaviors are quite different, it is not a best choice to try to bind them together and force them to undergo the same coordinate transformations as a whole, like that in the Lorentz transformations. Furthermore, the Maxwell’s theory does not impose any limitations on the velocity of the electromagnetic waves. To assume that all objects cannot move faster than the light in the vacuum need more examinations. We have carefully checked the main experiment results that were considered as supporting the special relativity. Unfortunately, we found that the experimental results may have been misinterpreted. We here propose a Galilean-Newtonian-Maxwellian relativity, which can give the same or even better explanations to those experimental results.
分类： 其他 >> 综合 提交时间： 2023-03-12 合作期刊: 《Art & Design Research》
摘要： The film Coco was screened worldwide, triggering a movie-going frenzy by its deep humanistic heritage and perfect grasp of the films artistry. Not only did the film make a perfect comeback in China, but it also achieved a global cultural export, which to some extent depends on Pixars successful strategy of cross-cultural expression. Behind this stunning effect, the high restoration of traditional Mexican cultural elements, the anti-traditional performance of the theme of death and the international top technological level of animation production are all factors of the films success.
分类： 工程与技术科学 >> 工程与技术科学其他学科 提交时间： 2023-01-03 合作期刊: 《2022年第三届艺术设计、传播与工程科学研讨会》
摘要： This paper provides a systematic review of papers in children's furniture design research through the CiteSpace visualization tool. We analyzed 446 papers on this field of research from CNKI and found the most influential publications, authors, journals, and institutions. In addition, we explored the current status of hotspots in this research field and predicted the future development trend through the analysis of keywords and Burst Keywords. The results show that the research field of children's furniture design in China is divided into ten major clusters, which can be grouped into three research areas, namely, basic research on children's furniture design, child-oriented design concept, and principles of children's furniture design. The future trends of children's furniture design are safety, child-centred, and humanization. The analysis of the research results in this field through CiteSpace software can enhance the understanding of the research in this field and provide a partial reference for the future research field of children's furniture design.
分类： 管理学 >> 管理学其他学科 提交时间： 2022-11-22 合作期刊: 《2022年第三届传播、创新和经济管理国际研讨会》
摘要： Based on the rapid development of the Internet era, Internet memes as a form of information visualization have shown implosive development and viral spread, and gradually evolved into a collective carnival within online communities. This study takes the group communication mechanism of memes in the process of group emoji competition as the entry point, and uses a questionnaire survey as the research method to initially explore the psychological motivation and communication mechanism of group communication of Internet memes. It is found that psychological motivation plays a primary role in the group communication mechanism of Internet memes; group ecology is a limiting factor in the communication of Internet memes; and group members' attitudes toward the use of memes can accelerate the spread of Internet memes.
分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： Hydrostatic leveling system (HLS) is widely used in precision engineering survey, especially the alignment of particle accelerator, and the tidal effects on the measurement accuracy of HLS is non-ignorable, thus studies on tidal effects on the HLS is vital. A set of HLS was installed in Jingxian seismostation for verifying the methods to handle the tidal effects on the readings of HLS. Harmonic analysis of the data recorded by HLS and DSQ water tube clinometers in Jingxian seismostation and contrastive analysis of the results are completed. The tilt tide can be well reflected in the data of the both instruments and the results are both reliable. The reasons of the difference between the results are analyzed in this paper. Besides, a validation study based on the measurement data of the HLS used in SPring-8 storage ring for tidal correction on the reading of HLS is completed. The research establishes a foundation for HLS to be applied in micron-level precision alignment of particle accelerator in the future.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： A maximum likelihood method is used to deal with the combined estimation of multi-measurements of a branching ratio, where each result can be presented as an upper limit. The joint likelihood function is constructed using observed spectra of all measurements and the combined estimate of the branching ratio is obtained by maximizing the joint likelihood function. The Bayesian credible interval, or upper limit of the combined branching ratio, is given in cases both with and without inclusion of systematic error.
分类： 物理学 >> 地球物理学、天文学和天体物理学 提交时间： 2024-02-01 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： Seeing is an important index to evaluate the quality of an astronomical site. To estimate seeing at the Muztagh-Ata site with height and time quantitatively, the European Centre for Medium-Range Weather Forecasts reanalysis database (ERA5) is used. Seeing calculated from ERA5 is compared consistently with the Differential Image Motion Monitor seeing at the height of 12 m. Results show that seeing decays exponentially with height at the Muztagh-Ata site. Seeing decays the fastest in fall in 2021 and most slowly with height in summer. The seeing condition is better in fall than in summer. The median value of seeing at 12 m is 0.89 arcsec, the maximum value is 1.21 arcsec in August and the minimum is 0.66 arcsec in October. The median value of seeing at 12 m is 0.72 arcsec in the nighttime and 1.08 arcsec in the daytime. Seeing is a combination of annual and about biannual variations with the same phase as temperature and wind speed indicating that seeing variation with time is influenced by temperature and wind speed. The Richardson number Ri is used to analyze the atmospheric stability and the variations of seeing are consistent with Ri between layers. These quantitative results can provide an important reference for a telescopic observation strategy.
分类： 地球科学 >> 地球科学其他学科 提交时间： 2017-12-08 合作期刊: 《干旱区科学》
摘要： The farming–pastoral ecotone in northern China is an extremely fragile ecological zone where wind erosion of cropland and rangeland is easy to occur. In this study, using a portable wind tunnel as a wind simulator, we conducted field simulated wind erosion experiments combined with laboratory analysis to investigate wind erosion of soils in trampled rangeland, non-tilled cropland and tilled cropland in Yanchi County, China. The results showed that compared with rangeland, the cropland had a higher soil water holding capacity and lower soil bulk density. The wind erosion rate of trampled rangeland was much higher than those of non-tilled cropland and tilled cropland. For cropland, the wind erosion rate of the soil after tilling was surprisingly less than that of the soil before tilling. With increasing of wind speed, the volume mean diameter of the eroded sediment collected by the trough in the wind tunnel generally increased while the clay and silt content decreased for all soils. The temporal variation in wind erosion of the trampled rangeland indicated that particle entrainment and dust emission decreased exponentially with erosion time through the successive wind erosion events due to the exhaustion of erodible particles.
分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： Coherent light with orbital angular momentum (OAM) is of great interest. Recently, OAM light generation by coupling a relativistic electron beam with a Gaussian mode laser pulse at the high harmonics of a helical undulator has been demonstrated experimentally. In this paper, the possibility of delivering coherent OAM light at the 3rd harmonic of the Gaussian mode seed laser is discussed for the Shanghai deep ultraviolet free-electron laser (SDUV-FEL). Considerations are given on the experiment setup, the expected performance and the possible measurement method.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Hyperentanglement~(HE), the simultaneous entanglement between two particles in more than one degrees of freedom, is relevant to both fundamental physics and quantum technology. Previous study on HE has been focusing on photons. Here, we study HE in individual neutral atoms. In most alkaline-earth-like atoms with two valence electrons and a nonzero nuclear spin, there are two stable electronic states, the ground state and the long-lived clock state, which can define an electronic qubit. Meanwhile, their nuclear spin states can define a nuclear qubit. By the Rydberg blockade effect, we show that the controlled-Z~(C$_{\text{Z}}$) operation can be generated in the electronic qubits of two nearby atoms, and simultaneously in their nuclear qubits as well, leading to a C$_{\text{Z}}\otimes$C$_{\text{Z}}$ operation which is capable to induce HE. The possibility to induce HE in individual neutral atoms offers new opportunities to study quantum science and technology based on neutral atoms.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Entanglement between atoms and microwave photons in a superconducting coplanar waveguide~(SCW) can enable hybrid quantum devices and interface static and flying qubits. We study a one-step controlled-Z~(C$_{\text{Z}}$) gate between a neutral atom trapped near a SCW and a microwave mode in the SCW, which is an extension of the gate proposed in [J. D. Pritchard, et.al., Phys. Rev. A 89, 010301(R) (2014)]. The gate protocol is simple and requires one laser pulse for exciting a transition between the ground and Rydberg states of the neutral atom.
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