Cosmic-ray positrons: are there primary sources?

Galactic cosmic rays consist of primary and secondary particles. Primary cosmic rays are thought to be energized by first order Fermi acceleration processes at supernova shock fronts within our Galaxy. The cosmic rays that eventually reach the Earth from this source are mainly protons and atomic nuclei, but also include electrons. Secondary cosmic rays are created in collisions of primary particles with the diffuse interstellar gas. They are relatively rare but carry important information on the Galactic propagation of the primary particles. The secondary component includes a small fraction of antimatter particles, positrons and antiprotons. In addition, positrons and antiprotons may also come from unusual sources and possibly provide insight into new physics. For instance, the annihilation of heavy supersymmetric dark matter particles within the Galactic halo could lead to positrons or antiprotons with distinctive energy signatures. With the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have measured the abundances of positrons and electrons at energies between 1 and 50 GeV. The data suggest that indeed a small additional antimatter component may be present that cannot be explained by a purely secondary production mechanism. Here we describe the signature of the effect and discuss its possible origin.     

Cyclic behavior of natural organic clay under variable confining pressure that match traffic loading conditions

ABSTRACT

One-way cyclic loading is more typical for traffic loading and cyclic triaxial test has been recognized as a useful method for solving many engineering problems. Under traffic loading, the influence of variable confining pressure on cyclic behavior of natural organic clay subjected to cyclic traffic loading is rarely reported in the literature. In this study, a laboratory investigation on undrained cyclic behavior of natural organic clay is presented and conducted by cyclic triaxial apparatus. Tests are conducted by both constant confining pressure and variable confining pressure, to simulate the loading conditions induced by passing vehicles in actual engineering. Different stress levels are also considered in this study. By comparing between the results of constant confining pressure tests and variable confining pressure tests, it shows that the one-way cyclic behavior of organic clay is influenced significantly by variation of confining pressure, in terms of pore water pressure, permanent axial strain and stress–strain hysteretic loops.     

Velocity-Interface Structure of the Southwestern Ryukyu Subduction Zone from EW9509-1 OBS/MCS Data

A wide-angle seismic survey, combining ocean-bottom seismometers (OBS) and multi-channel seismic (MCS) profiling, was implemented in the southwestern Ryukyu subduction zone during August and September 1995. In this paper, we present the data analysis of eight OBSs and the corresponding MCS line along profile EW9509-1 from this experiment. Seismic data modeling includes identification of refracted and reflected arrivals, initial model building from velocity analysis of the MCS data, and simultaneous and layer-stripping inversions of the OBS and MCS arrivals. The velocity-interface structure constructed along profile EW9509-1 shows that the northward subduction of the Philippine Sea Plate has resulted in a northward thickening of the sediments of the Ryukyu Trench and the Yaeyama accretionary wedge north of the trench. The boundary between the subducting oceanic crust and the overriding continental crust (represented by a velocity contour of 6.75 km/s) and a sudden increase of the subducting angle (from 5 degrees to 25 degrees) are well imaged below the Nanao Basin. Furthermore, velocity undulation and interface variation are found within the upper crust of the Ryukyu Arc. Therefore, the strongest compression due to subduction and a break-off of the slab may have occurred and induced the high seismicity in the forearc region. This revised version was published online in November 2006 with corrections to the Cover Date.     

A System for Fast Cartographic Sounding Selection

Soundings on nautical charts provide information about the shape of the ocean bottom between chart depth curves. A single chart may have thousands of soundings posted on it. This article describes a system for automatic cartographic sounding selection. In this system, a new algorithm for automated selecting soundings is developed. The algorithm is employed in such a way that it can guarantee (a) fast and accurate selecting sounding, (b) processing the circular depth curves, (c) solving the overplotting problems between depth curves and soundings, and (d) keeping selected soundings “prettier.” The system was intensively tested using real data sets, and its superiority has been revealed by the testing results.     

Traveling wavefront ray tracing and its applications

The current discussion of whether marine geodesy is something entirely new or part of oceanography or geodesy can be clarified by re‐examining our notions about the basic business of geodesy. This paper contends that the same basic geodetic services, which were needed for millenia to chart and control new territory, are being adapted now to the marine environment to suit modern accuracy standards. In a brief historical review it is shown that conceptually, the oceanic regions were always an integral part of geodetic concern. The oceans were certainly part of the world for the ancient map makers and for Pythagoras’ spherical earth model. Notions connected with the marine geoid were implied in ancient speculations. Distances and directions at sea, even depths, were determined to meet the requirements of the times. With the modern sophistication in geodetic theory and measuring techniques, these ideas became more refined and demanding in turn, but they were there all the time. For obvious reasons, land geodesy developed faster; marine geodesy will catch up now, because only now there is the technical capability and also an urgent economic motivation.     

养殖大黄鱼在自然海区降温不同阶段抗氧化水平及血清酶活性的变化

为了解越冬期间水温下降对大黄鱼抗氧化水平和血清酶活性的影响, 作者研究了养殖大黄鱼(Pseudosciaena crocea)冬季海区自然降温不同阶段(20、16、12、10、8℃)肝脏和肌肉中抗氧化水平及血清酶活性的变化。结果显示: 自然降温过程中, 肝脏中3 种抗氧化酶变化趋势不同, 其中SOD 活性呈升高趋势, 8℃时SOD活性最强; POD 活性呈先升高后降低的变化趋势, 16℃时活性最高; CAT 活性呈下降趋势; 而肌肉中这3 种抗氧化酶活性均呈下降趋势。肝脏中GSH 和MDA 含量在16℃时最高; 肌肉中的3 种抗氧化酶活性、GSH 和MDA 含量以及总抗氧化能力(T-AOC)均明显低于肝脏中, 反映了肝脏对清除自由基具有重要作用, 在抗氧化调节方面起到主要作用。血清酶ALT、AST、ALP、LDH 及CK-MB 随水温自然下降酶活性均呈现降低趋势, 即20℃时酶活性最强; CK 和LIP 随着水温降低, 呈先上升再下降的趋势; ADA 和GGT 随水温降低活性呈上升趋势。血清酶的不同变化, 说明水温对大黄鱼血清酶活性有一定的影响。     

莫尔圆极点确定的新方法

莫尔圆在岩土材料的强度理论、应力路径以及地基承载力等方面具有广泛的应用。极点是莫尔应力圆上的一个特殊点,具有惟一性,通过极点,可以求得任意分析平面的应力状态。特别是对于求解复杂状态下的应力问题,莫尔圆极点法具有简便、快捷的优点。提出了定义极点的新方法--射线法,利用应力隔离体力的平衡法则证明了该方法定义极点的正确性及惟一性,并且发现定义极点的平行线法和法线法是射线法的两种特殊情况。通过比较,发现不同方法所得到的极点位置并不相同,但求得的任意面上的应力状态是相同的,而且平行线法更便于使用。然而,所提出的射线法能加深对莫尔圆极点的理解,从而进一步推动其广泛应用。     

全球氦气勘探开发进展与利用现状

【研究目的】 由于氦气具有独特的物理特性,在科学研究、医学和高科技行业的用途越来越广泛。寻找更多的氦气资源,满足市场需求,是地质行业的责任。【研究方法】 按照统计分析原则,对全球氦气勘探成果与供需形势进行梳理、总结。【研究结果】 全球氦气资源分布极不均匀,主要氦气供应国为美国、卡塔尔、俄罗斯等。近期,许多公司开始在北美地区、俄罗斯、卡塔尔、坦桑尼亚等地开展氦气的勘探开发,其中北美部分地区的氦气资源位于富含氮气的储层中,具有广阔的开发前景,全球氦气勘探活动掀起新一轮热潮。【结论】 2021年全球氦市场出现供应缺口,当今全球氦气需求的增长开始转向亚洲和中东。建议高度重视氦气不可再生性和不可替代性,开展氦气资源潜力评价工程,勘查国内非烃类氦气矿床前景,加强国际合作,开展国内氦气储备地下空间评价与选址工作,增强中国的氦气储备能力。