分类： 地球科学 >> 地理学 提交时间： 2019-08-30 合作期刊: 《干旱区科学》
摘要： Riverine sand dunes develop as a result of fluvial-aeolian interactions. The primarily barchan dune chains along the Xiangshui River (a branch of the Xar Moron River in the western part of the Horqin Sandy Land of China) form a typical riverine dune field. We collected a series of samples from the riverine sand dunes parallel to the direction of the prevailing wind and investigated the sand sources and formation mechanisms of these dunes by determining the grain size, heavy mineral content and optically stimulated luminescence (OSL) of the samples. The sand of the near-river dunes was coarser than the sand of the dunes distant from the river, indicating that coarse sand of the valley mainly deposited on near-river dunes. The heavy mineral analysis suggested that wind-sand activity levels were intense on the upwind dunes, but relatively weak on the downwind dunes. This indicated that the sand sources for the near-river dunes were more abundant than those of the distant dunes. Our OSL analysis of samples suggested that the deposition rates on dunes near the river were greater than the deposition rates on dunes distant from the river. The development of dunes along the river indicated that the river played an important role in dune formation and development. In addition, airflow fluctuation and the formation of the waveform dunes had a type of feedback relationship. Grain size, heavy mineral and OSL analyses are widely used methods in wind-sand research. Sand dune grain size characteristics reflect the effects of airflow on the transport and separation of sand materials, as well as the physical characteristics of the sand sources. Heavy mineral characteristics are often used to investigate the relationships between sediments and sand sources. OSL indicates dune age, revealing formation of dunes. Therefore, it is useful to explore dune sand sources, as well as the mechanisms underlying dune formation, by determining grain size, heavy mineral content and OSL. This study investigated the sand sources of riverine dunes and provided new information about riverine dune formation and development.
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： The AP1000 with high safety is a generation III pressurized water reactor (PWR), its significant feature is passive safety system. However, its passive cooling can only maintain for 72 h and requires additional support from inside or outside the plant. To solve this problem, this study utilized the WGOTHIC software to calculate and analyze the water inventory in the passive containment cooling water tank under different conditions. The results show that when the cooling water inventory is 6553.78 m3, the AP1000 nuclear power plants can achieve long-term, completely passive cooling without any inside or outside the plant. The same outcomes occur when 65-mm-thick containment wall increases the design pressure rating to 0.6 MPa at the cooling water inventory of 5673 m3. Also, the AP1000 shield building was accordingly improved. An ANSYS analysis of the structural stability of the shield building with a 6000 m3 cooling water inventory confirmed that the new design can meet the requirements of the seismic design and the safe residual heat removal requirements of a large-scale PWR.
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： Synchrotron radiation (SR) represents a unique and innovative anti-cancer treatment due to its unique physical features, including high flux density, and tunable and collimated radiation generation. The aim of this work is to assess the dosimetric properties of SR in Shanghai Synchrotron Radiation Facility (SSRF) for potential applications to clinical radiation oncology. The experiments were performed with 34 and 50 keV X-rays on the BL13W biomedical beamline of SSRF and the 6 MV X-rays from ARTISTE linac for the dosimetry study. The percentage depth dose (PDD) and the surface dose of the SR X-rays and the 6 MV photon beams were performed in solid water phantom with Gafchromic EBT3 films. All curves are normalized to the maximum calculated dose. The depth of full dose buildup is about 10 m deeper for the monoenergetic X-ray beams of 34 and 50 keV. The beam transmits through the phantom, with a linear attenuation coefficient. The profile in the horizontal plane shows that the dose distribution is uniform within the facula, while the vertical profile shows a Gaussian distribution of the dose. The penumbra is less than 0.2 mm in the horizontal profile. Gafchromic EBT film may be a useful and convenient tool for dose measurement and quality control for the high space and density resolution. It is therefore important to gain a thorough understanding about the physical features of SR before this novel technology can be applied to clinical practice.
分类： 地球科学 >> 地理学 提交时间： 2022-10-14 合作期刊: 《干旱区科学》
摘要：The study of wind erosion processes is of great importance to the prevention and control of soil wind erosion. In this study, three structurally intact soil samples were collected from the steppe of Inner Mongolia Autonomous Region, China and placed in a wind tunnel where they were subjected to six different wind speeds (10, 15, 17, 20, 25, and 30 m/s) to simulate wind erosion in the wind tunnel. After each test, the soil surfaces were scanned by a 3D laser scanner to create a high-resolution Digital Elevation Model (DEM), and the changes in wind erosion mass and microtopography were quantified. Based on this, we performed further analysis of wind erosion-controlling factors. The study results showed that the average measurement error between the 3D laser scanning method and weighing method was 6.23% for the three undisturbed soil samples. With increasing wind speed, the microtopography on the undisturbed soil surface first became smooth, and then fine stripes and pits gradually developed. In the initial stage of wind erosion processes, the ability of the soil to resist wind erosion was mainly affected by the soil hardness. In the late stage of wind erosion processes, the degree of soil erosion was mainly affected by soil organic matter and CaCO3 content. The results of this study are expected to provide a theoretical basis for soil wind erosion control and promote the application of 3D laser scanners in wind erosion monitoring.
分类： 地球科学 >> 空间物理学 提交时间： 2016-12-22
摘要： We study competition between s-wave order and d-wave order through two holographic superconductor models. We find that once the coexisting phase appears, it is always thermodynamically favored, and that the coexistence phase is narrow and one condensate tends to kill the other. The phase diagram is constructed for each model in terms of temperature and the ratio of charges of two orders. We further compare the behaviors of some thermodynamic quantities, and discuss the different aspects and identical ones between two models.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-09
摘要： We construct a holographic multi-band superconductor model with each complex scalar field in the bulk minimally coupled to a same gauge field. Taking into account the back reaction of matter fields on the background geometry and focusing on the two band case with two scalar order parameters, we find that depending on the strength of the back reaction and the charge ratio of the two bulk scalars, five different superconducting phases exist, and three of five phases exhibit some region where both orders coexist and are thermodynamically favored. The other two superconducting phases have only one scalar order. The model exhibits rich phase structure and we construct the full diagram for the five superconducting phases. Our analysis indicates that the equivalent attractive interaction mediated by gravity between the two order parameters tends to make the coexistence of two orders much more easy rather than more difficult.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2018-05-18 合作期刊: 《干旱区科学》
摘要： The measurement and assessment of dust emissions from different landforms are important to understand the atmospheric loading of PM10 (particulate matter 10 m aerodynamic diameter) and to assess natural sources of dust; however, the methodology and technique for determining the dust still present significant research challenges. In the past, specialized field observation and field wind tunnel studies have been used to understand the dust emission. A series of wind tunnel tests were carried out to identify natural sources of dust and measure the magnitudes of dust emissions from different landforms. The method used in this study allowed the measurement of the PM10 emission rate using a laboratory based environmental boundary layer wind tunnel. Results indicated that PM10 emissions demonstrated strong temporal variation and were primarily driven by aerodynamic entrainment. Sand dunes, playa, and alluvial fans had the largest dust emission rates (0.85.4 mg/(m2s)) while sandy gravel, Gobi desert and abandoned lands had the lowest emission rates (0.0030.126 mg/(m2s)). Dust emissions were heavily dependent on the surface conditions, especially the availability of loose surface dust. High dust emissions were a result of the availability of dust-particle materials for entrainment while low dust emissions were a result of surface crusts and gravel cover. Soil surface property (surface crusts and gravel cover) plays an important role in controlling the availability of dust-sized particles for entrainment. The dust emission rate depended not only on the surface conditions but also on the friction velocity. The emission rate of PM10 varies as a power function of the friction velocity. Although dynamic abrasion processes have a strong influence on the amount of dust entrainment, aerodynamic entrainment may provide an important mechanism for dust emissions. Large volumes of dust entrained by aerodynamic entrainment can not only occur at low shear velocity without saltation, but may dominate the entrainment process in many arid and semi-arid environments. So it may also be responsible for large magnitude dust storms. Playa and alluvial fan landforms, prior to developing a surface crust, may be the main sources of dust storms in Qinghai Province.
分类： 生物学 >> 动物学 提交时间： 2022-01-24 合作期刊: 《古脊椎动物学报》
摘要： Currently, there are still different views regarding the chronology of the Late Cenozoic deposits in the Nihewan Basin, which results from the contradiction between biostratigraphic correlations based on mammalian fossils and magnetostratigraphic dating results. Biostratigraphic correlations indicate that the aeolian red clay exposed in the Sanggan River canyon, the fluviolacustrine red clay with sands and gravels, and the sandy clay of swamp facies on both sides of the lower reaches of the Huliu River belong to the Upper Pliocene, whereas the magnetostratigraphic dating usually correlates them to the Lower Pleistocene. In October 2011, a collection of mammalian fossils was unearthed from a block of collapsed deposits at Yegou in the Nihewan Basin, which is about 300 m north of the Laowogou section that is well known for the Pliocene mammalian fossils from its lower part. The Yegou fossils are identified herein as 10 species in 9 genera: Nyctereutes tingi, N. sinensis, Pachycrocuta pyrenaica, Homotherium sp., Hipparion (Plesiohipparion) houfenense, Dicerorhinus sp., Muntiacus sp., Axis shansius, Gazella blacki, and Paracamelus sp. The fauna is quite different from the classic Early Pleistocene Nihewan Fauna in composition and provides new evidence for the existence of the Upper Pliocene in the Nihewan Basin. Based on a systematic description of the fauna, its composition and geological age are discussed, and the compositional features of large mammals of the Late Pliocene and the Early Pleistocene mammalian faunas in the Nihewan Basin are summarized.
分类： 生物学 >> 生物物理学 >> 细胞生物学 提交时间： 2016-05-11
Zhu, Lei
Yang, Jing-Yu
Dong, Ying-Xu
Liu, Yang
Miao, Feng-Rong
Xue, Hong
Wu, Chun-Fu
Xue, Hong
Xue, Xue
Wang, Yong-Feng
摘要： In Alzheimer's disease (AD), activated microglia invade and surround beta-amyloid plaques, possibly contributing to the aggregation of amyloid beta (A beta), which affect the survival of neurons and lead to memory loss. Phosphodiesterase-5 (PDE-5) inhibitors have recently been shown a potential therapeutic effect on AD. In this study, the effects of yonkenafil (yonk), a novel PDE-5 inhibitor, on cognitive behaviors as well as the pathological features in transgenic AD mice were investigated. Seven-month-old APP/PSI transgenic mice were treated with yonk (2, 6, or 18 mg/kg, intraperitoneal injection (i.p.)) or sildenafil (slid) (6 mg/kg, i.p.) daily for 3 months and then behavioral tests were performed. The results demonstrated that yonk improved nesting-building ability, ameliorated working memory deficits in the Y-maze tasks, and significantly improved learning and memory function in the Morris water maze (MWM) tasks. In addition, yonk reduced the area of A beta plaques, and inhibited over-activation of microglia and astrocytes. Furthermore, yonk increased neurogenesis in the dentate granule brain region of APP/PSI mice, indicated by increased BrdU(+)/NeuN(+) and BrdU(+)/DCX+ cells compared to vehicle-treated transgenic mice. These results suggest that yonk could rescue cognitive deficits by ameliorated amyloid burden through regulating APP processing, inhibited the over-activation of microglia and astrocytes as well as restored neurogenesis. (C) 2015 Elsevier Ireland Ltd. All rights reserved.
提交时间： 2017-05-02
Shan, L [Shan, Lei][ 1,2 ]
Wang, YX [Wang, Yong-xin][ 1 ]
Li, JL [Li, Jin-long][ 1 ]
Li, H [Li, He][ 1 ]
Lu, X [Lu, Xia][ 1 ]
Chen, JM [Chen, Jian-min][ 1 ]
摘要： A Cr/Cr2N/CrN multilayer coating with a thickness of 24.4 mu m was deposited by multi-arc ion plating. The coating was systematically characterized by field emission scanning electron microscopy [FESEM], X-ray photoelectron spectrometry [XPS], energy disp
分类： 生物学 >> 生物物理学 提交时间： 2016-05-12
Wei, Ming-Yu
Xue, Lu
Tan, Li
Sai, Wen-Bo
Liu, Xiao-Cao
Jiang, Qiu-Ju
Shen, Jinhua
Peng, Yong-Bo
Zhao, Ping
Yu, Meng-Fei
Chen, Weiwei
Ma, Li-Qun
Liu, Qing-Hua
Wei, Ming-Yu
Xue, Lu
Tan, Li
Sai, Wen-Bo
Liu, Xiao-Cao
Jiang, Qiu-Ju
Shen, Jinhua
摘要： The participation of large-conductance Ca2+ activated K+ channels (BKs) in chloroquine (chloro)-induced relaxation of precontracted airway smooth muscle (ASM) is currently undefined. In this study we found that iberiotoxin (IbTx, a selective inhibitor of BKs) and chloro both completely blocked spontaneous transient outward currents (STOCs) in single mouse tracheal smooth muscle cells, which suggests that chloro might block BKs. We further found that chloro inhibited Ca2+ sparks and caffeine-induced global Ca2+ increases. Moreover, chloro can directly block single BK currents completely from the intracellular side and partially from the extracellular side. All these data indicate that the chloro-induced inhibition of STOCs is due to the blockade of chloro on both BKs and ryanodine receptors (RyRs). We also found that low concentrations of chloro resulted in additional contractions in tracheal rings that were precontracted by acetylcholine (ACH). Increases in chloro concentration reversed the contractile actions to relaxations. In the presence of IbTx or paxilline (pax), BK blockers, chloro-induced contractions were inhibited, although the high concentrations of chloro-induced relaxations were not affected. Taken together, our results indicate that chloro blocks BKs and RyRs, resulting in abolishment of STOCs and occurrence of contraction, the latter will counteract the relaxations induced by high concentrations of chloro.
点击量
点击量
下载量
评论
通过
待评议
