巷道围岩状态的等效应力等效应变表述

在体积应变为零的条件下,根据巷道围岩属简单加载的特性得到围岩中同时关联三向应力 , , 和三向应变 , , 的,用等效应力 和等效应变 表示的对围岩加载-形变关系式。严格地论证了巷道围岩的弹性、硬化、软化和流动区的应力应变状态分别与围岩的等效应力-等效应变曲线各阶段的应力应变状态相对应。以等效应力、等效应变为中间变量可以简化围岩弹性分析,简捷地写出巷道围岩偏应力应变能的计算公式。等效剪应力 是围岩中的最大剪应力 ,等效剪应力单元受正应力和剪应力作用,但其上只有剪切应变,这突出了巷道围岩形变破坏是由于最大剪应力和偏应力应变能所致的实质。根据等效剪应力概念确定的滑移线,可适用于材料应变硬化和软化阶段,不要求刚塑性假定条件。     

2015—2020年中国土地利用变化遥感制图及时空特征分析

持续地开展国家尺度土地利用/覆盖变化遥感监测对于新时代国土空间规划和“美丽中国”蓝图绘制具有重要的科学价值。本文采用Landsat 8 OLI、GF-2等卫星遥感数据,融合遥感大数据云计算和专家知识辅助人机交互解译方法,研发了中国土地利用变化（2015—2020年）和2020年土地利用现状矢量数据（CLUD 2020）,建立了完整的30 a（20世纪80年代末—2020年）每隔5 a的30 m分辨率中国土地利用动态数据库。基于CLUD 2020数据,从全国和区域两个尺度揭示了2015—2020年中国土地利用变化的总体规律、区域分异和主要特征。研究表明：将遥感大数据云计算生成的30 m分辨率植被覆盖变化和地表类型变化检测信息融入到人机交互遥感解译方法,可有效地提高大范围土地利用变化遥感制图的效率和变化图斑辨识的准确性;精度评价表明,CLUD 2020一级类型制图的综合精度达95%。总体上,全国范围内国土空间开发强度与2010—2015年比较进入相对稳定状态。期间全国耕地面积仍保持减少态势,空间分异特征为耕地南减北增,东北松嫩平原及其与三江平原交界区大规模的旱地向水田转移,西北新疆南部开垦和北部退耕/撂荒并存;全国城乡建设用地持续增加,空间分异特征表现为由以往的沿海地区和超大、大城市集聚转向中西部地区的大中小城镇周边蔓延为主。全国范围的林草自然生态用地面积持续减少,但强度与2010—2015年比较有所下降;受气候变化的持续影响,青藏高原地区的河流湖泊等水域面积显著增加。以上土地利用变化格局与“十三五”期间国家高质量发展、生态文明建设宏观战略和气候变化的影响密切相关。     

近10年新疆积雪面积时空变化研究

区域尺度积雪信息的时空监测对确定雪灾的影响范围及灾情等级划分具有重要意义。本文利用近10年的MODIS积雪产品,按月最大面积的规则合成;分析了新疆积雪覆盖面积的时空变化特征,结果表明:时间上,新疆积雪面积有减少的趋势。空间上,近10年新疆积雪季节内永久性积雪覆盖区域主要分布在阿勒泰山脉、天山北麓及沿昆仑山脉西南部。其中天山及阿尔泰山之间的河谷及盆地的草原积雪面积波动主导了新疆整体积雪总面积的波动。     

Unemployment in Non-Metropolitan Australia: integrating geography,social and individual contexts

Despite a significant period of strong economic and jobs growth nationally, there is well-established evidence in Australia that the proceeds of this growth have not been shared equally, either between places or between individuals. Empirically, it is well known that particular socioeconomic groups have a higher risk of unemployment and it has become equally well established that there are particular geographic patterns of labour market disadvantage that suggest that local geographic context is also important. What is not well understood are the ways in which phenomena at the geographic level are associated with individual-level characteristics and other social contexts in ways that negatively impact on a range of social outcomes, including unemployment. The present paper specifically addresses this issue by using a multi-scalar approach and using survey data from the Housing, Income and Labour Force Dynamics Australia (HILDA) survey and aggregate level census data to model unemployment risk. The paper argues that to better understand unemployment and to add to sound policy development, approaches that incorporate a variety of contexts, including the impact of local geographies, are important.     

Theoretical interpretation of photometric properties of the Martian surface and atmosphere

Earth-based UBV photometry, high-quality photographs from the Lowell Observatory collection, and Mariner 9 data have been combined with a new radiative transfer theory to derive physical parameters for the Martian surface and atmosphere, both before and during the 1971 dust storm. We find that the dust particles of the storm had a single-scattering albedo of 0.84 ± 0.02 and an asymmetry factor of 0.35 ± 0.10 in green (V) light. The geometric albedo of Mars was 0.15 and the phase integral 1.83, which yield 0.27 for the Bond albedo. The mean optical thickness of the “clear” atmosphere averaged over the whole planet was 0.15 ± 0.05 and was not detectably dependent on wavelength. Geometric albedos for the surface are 0.25 (light areas) and 0.17 (dark areas) in V, 0.095 in B (both areas), and 0.060 in U (both areas). The soil particles are moderately backward scattering with an asymmetry factor of ?0.20, indicating them to be rather opaque. The mean surface roughness, on a scale larger than that of individual dust particles and therefore large compared with the wavelength, is 0.57. This represents the depth/radius ratio of an average hole and it is only one-half as large as values typical for the Moon and asteroids.     

Saturn's Rings: Azimuthal variations,phase curves,and radial profiles in four colors

Four-color photographic photometry of Saturn for the 1977–1979 apparitions has been analyzed to determine the dependence of ring brightness on wavelength, solar phase angle, ring particle orbital phase angle (azimuthal effect), declination of the Earth relative to the ring plane (tilt angle), and radial distance from Saturn. Azimuthal brightness variations up to ±20% relative to the ansae are clearly apparent for the maximum of ring A, but are not detectable for ring B or the outer portion of ring A. The shape of the intensity (I) versus orbital phase angle (θ) curve varies with ring tilt (B) and probably with wavelength, and shows 180° symmetry. As characterized by its slope near the ansae, this curve suggests that the azimuthal effect increases as B decreases from 26 to ≈11°. The phase curves l(α) for the ansae show very little dependence on ring tilt (26° > B > 6°), on wavelength, or on radial distance from Saturn; possibly the curves are somewhat steeper at the smallest tilt angles and for ring A relative to ring B. The radial profile of both rings becomes flatter with decreasing tilt angle and with decreasing wavelength. The latter effect is a natural result of the classical, many-particle-thick ring model.     

Impulsive Flux Transfer Events and Solar Flares

Experimental and theoretical aspects of the fundamental process of magnetic flux transfer ('field line reconnection') are reviewed. Explosively rapid events are observed in a laboratory magnetoplasma device designed to test certain aspects of neutral point theories of the solar flare mechanism. In these events, ultra-fast release of magnetic energy through reconnection of field lines is effected by a conduction mode instability in which an abrupt upward transition to anomalous resistivity takes place in the neighbourhood of the X-point. The events are triggered when the X-point current density exceeds the conduction mode instability threshold. The energy that is released is that which is associated with the induced current system that supports field line reconnection under ordinary quiescent conditions. Many characteristics of the laboratory events and their associated phenomena, when appropriately scaled, show remarkable agreement with corresponding flare observational data. Some new directions for further development of flare theory are therefore recommended. These experiments indicate that a number of assumptions commonly made in theoretical analysis of the reconnection process are inappropriate. The flux transfer process can be well understood theoretically in terms of a simple circuit analogue which models the laboratory process.     

地震孕育、发生、发展动态过程的三维有限元数值模拟

为探讨用数值方法模拟地震孕育、发生、发展动态过程的途径,从线性流变体介质内制约质点运动的运动方程出发,导出了模拟地震孕育、发生、发展动态过程的三维有限元方程及程序。还给出了模拟进程中地震孕育、发生、发展过程的约束条件,使得可以用同一个程序完整地模拟地震孕育、发生、发展的全过程,为地震过程本质的认识以及物理预报的实现提供了一个潜在的新手段。     

High-resolution radio observations of Seyfert galaxies in the extended 12-μm sample – I. The observations

We present 8.4-GHz VLA A-configuration observations of 87 sources from the mid-infrared-selected AGN sample of Rush et al. These 0.25-arcsec-resolution observations allow elongated radio structures tens of pc in size to be resolved, and enable radio components smaller than 3.5 arcsec to be isolated from diffuse galactic disc emission. When combined with previous data, matched radio observations covering 90 per cent of the sample have been collected, and these represent the largest subarcsecond–resolution radio imaging survey of a homogeneously selected sample of Seyfert galaxies to date.
We use our observations to identify five radio-loud AGN in the sample. The nature of the radio emission from Seyfert nuclei will be discussed in subsequent papers.     

更新世冰盖与大洋碳储库相互作用的箱式模型模拟

全球大洋深海有孔虫碳同位素(δ13C)记录中广泛发现40万年周期,这一周期可能与偏心率长周期的轨道驱动有关.1.6 Ma以来,δ13C的这一长周期拉长到50万年,且重值期不再与偏心率低值对应.目前对δ13C 40万年周期的成因及其周期拉长的机制还不明确.这里使用了包含9个箱体的箱式模型,用于研究热带过程与冰盖相互作用及其对大洋碳循环的影响.模拟结果显示当北半球高纬海区海冰迅速增大时冰盖迅速融化,进入冰消期,而当海冰快速消失后,冰盖则重新缓慢增长.冰盖变化具有冰期长,间冰期短的非对称形态.在季节性太阳辐射量的驱动下冰盖变化具有10万年冰期-间冰期旋回.当冰盖融化速率受北半球高纬夏季太阳辐射量控制时,冰盖变化的岁差周期明显加强,相位与地质记录一致,说明轨道驱动可以通过非线性相位锁定机制使冰盖变化与其在相位上保持一致.海冰的阻隔效应使大气中CO₂在冰消期时增多.冰期时大洋环流减弱使大气中CO₂逐渐减少.当模型只有ETP驱动的风化作用而不考虑冰盖变化时,模拟的δ13C记录显示极强的40万年周期,体现了大洋碳储库对热带风化过程的响应.当同时考虑冰盖变化和风化作用时,模拟的δ13C结果中40万年周期减弱而10万年周期加强,并且40万年周期上碳储库与偏心率的相位与不考虑冰盖变化时的相位也存在差异,反映了冰盖变化引起的洋流改组压制了大洋碳循环对热带过程的响应.