分类: 地球科学 >> 地质学 提交时间: 2018-01-09 合作期刊: 《古脊椎动物学报》
摘要: An adult skull with articulated atlas and an adult mandible, collected by Emile Licent in 1920 from the Late Miocene of Qingyang (Gansu, China), is recognized as a new species Chilotherium licenti sp. nov. These specimens possess typical characters of the genus Chilotherium, such as the strongly expanded mandibular symphysis, the huge and dagger-shaped i2s with an upturned medial flange, strongly constricted protocones, well-developed crochet and crista, and weakly developed parastyle folds and paracone ribs. Chilotherium licenti is characterized by the near absence of lingual and buccal cingula, and the medifossette on P2 to M2 forming by well-developed crochet and crista. The derived characters of the new species indicate that it is the highly specialized taxon of the genus Chilotherium, corresponding to MN12-13 of the Turolian in Europe. Based on a phylogenetic analysis of rhinocerotids, C. licenti from the Late Miocene is the most derived species in the known species of the Chilotherium lineage.
分类: 地球科学 >> 地质学 提交时间: 2017-08-24 合作期刊: 《古脊椎动物学报》
摘要: 嵌齿象是真象的基干类群,其研究历来受到重视,同时也存在很多争议。维曼嵌齿象(Gomphotherium wimani)是中国的一个特有种,之前仅有一些牙齿和破碎下颌的报道,研究者对其形态特征和演化地位的认识一直比较模糊。本文报道了发现于甘肃省临夏盆地的维曼嵌齿象的新材料,包括上沟地点一件未成年头骨和倒黑沟地点属于同一个体的部分颊齿。通过研究对比,认为维曼嵌齿象是嵌齿象中一个比较进步的种,具有如下独有特征:颊齿的主齿柱前后中心小尖分裂并成嵴状,副齿柱趋向于分裂,发育有弱的副齿柱中心小尖,齿谷中等开阔,齿冠相对较高。对过去发现的维曼嵌齿象材料的厘定表明,该种最初建立时产于泉头沟地点的一颗m3实际上是葛氏铲齿象(Platybelodon grangeri)的M3; 而西宁吊沟地点发现的维曼嵌齿象的一件M3极有可能属于铲齿象类(amebelodontids)。对厘定后的维曼嵌齿象地点的研究表明,维曼嵌齿象分布于中国甘肃、青海的几个中中新统地点,其时代基本上可以与MN6−MN7/8早期相对比,时代跨度估计为15~13 Ma。
分类: 核科学技术 >> 裂变堆工程技术 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: Neutron-TPC (nTPC) is a fast neutron spectrometer based on GEM-TPC (Gas Electron Multiplier-Time Projection Chamber) and expected to be used in nuclear physics, nuclear reactor operation monitoring, and thermo-nuclear fusion plasma diagnostics. By measuring the recoiled proton energy and slopes of the proton tracks, the incident neutron energy can be deduced. It has higher n/ separation ability and higher detection efficiency than conventional neutron spectrometers. In this paper, neutron energy resolution of nTPC is studied using the analytical method. It is found that the neutron energy resolution is determined by 1) the proton energy resolution (Ep/Ep), and 2) standard deviation of slopes of the proton tracks caused by multiple Coulomb scattering (k(scattering)) and by the track fitting accuracy (k(fit)). Suggestions are made for optimizing energy resolution of nTPC. Proper choices of the cut parameters of reconstructed proton scattering angles (cut), the number of fitting track points (N), and the working gas help to improve the neutron energy resolution.
分类: 生物学 >> 动物学 提交时间: 2017-11-07 合作期刊: 《古脊椎动物学报》
摘要: Mammut is the terminal taxon of the proboscidean group Mammutidae, which survived to the Late Pleistocene. Although this genus was widely distributed in the Pliocene of Eurasia and the Pleistocene of North America, little is known about its early evolution. Here, we report on Mammut cf. M. obliquelophus from the Upper Miocene of northern China based on new fossil material, including an almost complete juvenile cranium and other remains, which show many primitive features within Mammutidae and clearly demonstrate the morphological evolution of Mammut. The strongly laterally expanded lateral wing of the occiput and the presence of basal constriction of the incisive fossa display cranial similarity between Mammut cf. M. obliquelophus and both Eozygodon morotoensis and Choerolophodon guangheensis, early representatives of the Mammutidae and Choerolophodontidae, respectively, indicating the close relationship between these two groups: both of them are located at the basal phylogenetic positions in Elephantimorpha. This result is further confirmed by a cladistic analysis.
分类: 生物学 >> 生物学其他学科 提交时间: 2018-07-18 合作期刊: 《古脊椎动物学报》
摘要: Here we discribe a new ootypes of prismatoolithids found from the Late Cretaceous Jiangjunding Formation in the Laiyang Basin, Shandong Province. On the basis of characters such as elongate ovoids, smooth eggshell surface, relatively thinner eggshell thickness, prismatic eggshell units, slender pores in radial section of eggshell and little pores with round or irregular shapes in tangeital section of eggshell, we erect one new oogenus and one new oospecies: Laiyangoolithus lixiangensis oogen. et oosp. nov. The discovery of L. lixiangensis not only enriches the diversity and composition of the Laiyang Dinosaur Egg Fauna, but the paleogeographic distribution of primatoolithids as well. In addition, it provides more paleontological materials for the study of the diversity and paleogeographic distribution of troodontids in China.
分类: 地球科学 >> 地质学 提交时间: 2017-08-08 合作期刊: 《古脊椎动物学报》
摘要: Mammut is the terminal taxon of the proboscidean group Mammutidae, which survived to the Late Pleistocene. Although this genus was widely distributed in the Pliocene of Eurasia and the Pleistocene of North America, little is known about its early evolution. Here, we report on Mammut cf. M. obliquelophus from the Upper Miocene of northern China based on new fossil material, including an almost complete juvenile cranium and other remains, which show many primitive features within Mammutidae and clearly demonstrate the morphological evolution of Mammut. The strongly laterally expanded lateral wing of the occiput and the presence of basal constriction of the incisive fossa display cranial similarity between Mammut cf. M. obliquelophus and both Eozygodon morotoensis and Choerolophodon guangheensis, early representatives of the Mammutidae and Choerolophodontidae, respectively, indicating the close relationship between these two groups: both of them are located at the basal phylogenetic positions in Elephantimorpha.This result is further confrmed by a cladistic analysis.
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: For a high-energy electron facility, estimates of induced radioactivity in materials are of considerable importance to ensure that the exposure of personnel and the environment remains as low as reasonably achievable. In addition, accurate predictions of induced radioactivity are essential to the design, operation, and decommissioning of a high-energy electron linear accelerator. In the case of the 200-MeV electron linac of the National Synchrotron Radiation Laboratory (NSRL), the electrons are accelerated by five acceleration tubes and collimated by copper scrapers. The scrapers, which play a vital role in protecting the acceleration cavity, are bombarded by many electrons over a long-term operation, which causes a significant amount of induced radioactivity. Recently, the NSRL Linac is the first high-energy electron linear accelerator in China to be out of commission. Its decommissioning is highly significant for obtaining decommissioning experience. This paper focuses on the measurement of induced radioactivity on the fourth scraper, where the electron energy was 158 MeV. The radionuclides were classified according to their half-lives. Such a classification provides a reliable basis for the formulation of radiation protection and facility decommissioning. To determine the high-radioactivity area and to facilitate the decommissioning process, the slicing method was applied in this study. The specific activity of 60Co in each slice was measured at a cooling time of ten months, and the results were compared with the predictions generated by Monte Carlo program FLUKA. The trend of the measured results is in good agreement with the normalized simulation results. The slicing simulation using Monte Carlo method is useful for the determination of high-radiation areas and proper material handling protocols and, therefore, lays a foundation for the accumulation of decommissioning experience.
分类: 核科学技术 >> 核探测技术与核电子学 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: A new electrode structure CdZnTe (Cadmium Zinc Telluride) detector named Binode CdZnTe has been proposed in this paper. Together with the softwares of MAXWELL, GEANT4, and ROOT, the charge collection process and its gamma spectrum of the detector have been simulated and the detector structure has been optimized. In order to improve its performance further, Compton scattering effect correction has been used. The simulation results demonstrate that with refined design and Compton scattering effect correction, Binode CdZnTe detectors is capable of achieving 3.92% FWHM at 122 keV, and 1.27% FWHM at 662 keV. Compared with other single-polarity (electron-only) detector configurations, Binode CdZnTe detector offers a cost effective and simple structure alternative with comparable energy resolution.
分类: 核科学技术 >> 辐射物理与技术 提交时间: 2024-04-25
摘要: A Laue microdiffraction beamline (BL03HB) was constructed at the Shanghai Synchrotron Radiation Facility (SSRF). This beamline features two consecutive focusing points in two different sectors within its end station, the first dedicated to protein crystallography and the other tailored to materials science applications. Based on a superbend dipole magnet with a magnetic field of 2.29 T, a two-stage focusing design was implemented with two sets of Kirkpatrick–Baez mirrors to achieve a micro white beam as small as 4.2×4.3 µm 2 at the first sector and 0.9×1.3 µm 2 at the second sector in the standard beamline operation mode at SSRF. The X-ray microbeam in the two sectors can be easily switched between monochromatic and white beams by moving a four-bounce monochromator in or out of the light path, respectively. In the protein crystallography sector, white-beam Laue microdiffraction was demonstrated to successfully determine the structure of protein crystals from only a few images of diffraction data collected by a Pilatus 2M area detector. In the materials science sector, the white-beam Laue diffraction was collected in a reflection geometry using another Pilatus 2M area detector, which could map the microstructural distribution on the sample surface by scanning the samples. In general,the BL03HB beamline promotes the application of Laue microdiffraction in both protein crystallography and materials science. This paper presents a comprehensive overview of the BL03HB beamline, end station, and the first commission results.
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: Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when magnetic field is applied parallel to the sample plane. By combining X-ray absorption near edge structure spectrum and positron annihilation lifetime spectroscopy, Ti3+-VO defect complexes (or clusters) have been identified in annealed crystals at high vacuum. We elucidate that the unpaired 3d electrons in Ti3+ ions provide the observed room-temperature ferromagnetism. Besides, excess oxygen ions in TiO2 lattice could induce a number of Ti vacancies which increase magnetic moments obviously.
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: Thermal aging effects on surface of 2.5 MeV Fe ion irradiated Fe-0.6%Cu alloy were investigated using positron annihilation techniques. The samples were irradiated at 573 K to a dose of 0.1 dpa. Their thermal aging was performed at 573 K for 5, 50, and 100 h. From the results of Doppler broadening measurement, an obvious trough could be seen in near surface region from the S parameters and inflection point form at S-W curves. This indicates changes in the annihilation mechanism of positrons in surface region after thermal aging. Coincident Doppler broadening indicates that the density of Cu precipitates in the thermal aged samples decreased, due to recovery of the vacancies. Keywords Fe-Cu alloy; Positron annihilation; Irradiation; Thermal aging
分类: 核科学技术 >> 核探测技术与核电子学 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: Resistive Plate Chambers (RPCs) built from a new type of Bakelite developed at Institute of High Energy Physics (IHEP), Chinese Academy of Sciences have been used in the BESIII Muon identification system for several years without linseed oil coating, but characteristic aging performances were observed. To adapt to the RPCs in the aging state, the front-end electronics have been upgraded by enhancing the front-end protection, improving the threshold setting circuit, and separating power supplies of the comparator and the field programmable gate array (FPGA). Improvements in system stability, front-end protection and threshold consistency have been achieved. In this paper, the system upgrade and the test results are described in detail.