Measurements of spectral lines observed with Hinode/EIS as implications for coronal heating

We have measured the line widths and nonthermal velocities in 12 solar regions using high resolution EUV data taken by Hinode/EIS. We find that there exists a positive correlation between the intensity and nonthermal velocity for the Fe XII emission line as well as some other lines. The correlation coefficients decrease from the disk center to the limb. However, the nonthermal velocities of a particular spectral line do not vary much in different regions, so they are considered isotropic. In particular, we find that for a coronal loop structure, the largest widths and nonthermal velocities occur at the footpoints, where outflows appear. Based on these observational results, we discuss several physical processes responsible for coronal heating.     

俯冲带库仑楔形体力学

楔形体理论研究楔形体在底部摩擦力、重力和边界外力共同作用下内部的应力状态,有助于我们定量分析断层强度和岩石性质与楔形体稳定状态之间的关系.本文首先简要介绍基于不同楔形体材料而得出的应力解析解.然后介绍基于理想弹塑性材料的俯冲带库仑楔应力解析解.最后介绍基于该解析解而提出的动态库仑楔形体理论.俯冲带地震反射剖面数据表明,...     

湘鄂西中生代弧形叠加扩展的变形记录

通过对湘鄂西构造带进行大量的构造形迹测量、解析,结合研究区内构造变形年龄数据的统计分析.明确燕山中期(J3—K1)早期弧形构造弧顶方向为330°,并向两侧发散状分布,以大别山、黔中、黄陵隆起为约束点,湘鄂西形成了由南东侧至北东侧构造迹线由NE→NEE→EW→NWW逐渐偏转的弧形构造,最大主应力方向偏转近114°.同时早...     

Brittle Rock Failure in the Steg Lateral Adit of the Lötschberg Base Tunnel

Summary  During the crossing of brittle rock formations at the L?tschberg base tunnel, failure phenomena have been observed both at the tunnel face and at the walls. A detailed analysis has been undertaken to explain these behaviours, based on the recent developments of Canadian research on brittle failure mechanisms. At the tunnel walls, a very good agreement is found between the calculated and observed damage and between two prediction methods, i.e. a semi-empirical failure criterion and elastic calculations with the “brittle Hoek-Brown parameters.” Near the face, due to the 3D nature of the stress conditions, some limitations of these approaches have been highlighted, and the growth of wall failure has been analysed. This research allowed a better understanding of the brittle rock mass behaviour at the L?tschberg base tunnel and showed that brittle failure processes dominate the behaviour of deep, highly stressed excavations in massive to moderately jointed rock. It also illustrates where improvements to the adopted approaches are required.     

Rock Stress,Rock Stress Measurements,and the Integrated Stress Determination Method (ISDM)

The primary objectives of this work are to (1) improve the understanding of the prevailing stress distribution at the Äspö Hard Rock Laboratory (HRL) in SE Sweden by employing an integrated stress determination approach, and in order to accomplish this (2) extend the existing stress integration methodology denominated integrated stress determination method (ISDM; Cornet in Comprehensive Rock Engineering vol 3, Pergamon Press, Oxford, pp 413–432, 1993a). The new developments of the ISDM involve a 12-parameter representation of the regional stress field in the rock mass (i.e., the full stress tensor and its variation with depth) that is applicable to hydraulic stress data (sleeve fracturing, hydraulic fracturing, and hydraulic tests on pre-existing fractures), overcoring data (CSIR- and CSIRO-type of devices), and to combinations of hydraulic and overcoring stress data. For the latter case, the elastic parameters of the overcoring technique may be solved in situ by allowing the hydraulic stress data to constrain them. As a result, the problem then involves 14 model parameters. Results from the study show that the ISDM effectively improves the precision of the prevailing stress field determination and that it is especially powerful for identification of consistencies/inconsistencies in an existing data set. Indeed, this is the very basic premise and goal of stress integration; combine all available data to achieve as complete a characterization of the mechanical stress model as possible, and not to identify a solution that fits only loosely the maximum amount of stress data.     

2019年四川长宁MS6.0地震前破裂区内视应力和b值的变化

视应力和b值都可以反映地壳应力变化。当应力增加时,视应力会增加,而b值降低。因此,应力变化将导致视应力和b值之间呈负相关关系,即,根据视应力和b值之间的负相关关系可以研究地壳构造应力的变化。本文利用2000年1月—2019年12月长宁M_S6.0地震破裂区内3.0≤M_L≤3.6地震的视应力和2.0≤M_L≤4.3地震目录,研究了视应力和b值随时间的变化,发现:2013年2月—2017年3月间,视应力呈趋势上升变化,历时约4年,在震前两年时间内,视应力仍维持在较高水平。在视应力呈趋势上升变化期间,b值则呈趋势下降变化。当视应力维持在较高水平时,b值则维持在较低水平。即,长宁M_S6.0地震发生前,破裂区内视应力增加,同时b值下降。这表明,2019年长宁M_S6.0地震发生前破裂区内存在明显的构造应力增加过程,对地震孕育过程的认识和地震预测研究都具有启示意义。      

Spectroscopic evidence of charge exchange X‐ray emission from galaxies

What are the origins of the soft X‐ray line emission from non‐AGN galaxies? XMM‐Newton RGS spectra of nearby non‐AGN galaxies (including starforming ones: M82, NGC 253, M51, M83, M61, NGC 4631, M94, NGC 2903, and the Antennae galaxies, as well as the inner bulge of M31) have been analyzed. In particular, the Kα triplet of O VII shows that the resonance line is typically weaker than the forbidden and/or inter‐combination lines. This suggests that a substantial fraction of the emission may not arise directly from optically thin thermal plasma, as commonly assumed, and may instead originate at its interface with neutral gas via charge exchange. This latter origin naturally explains the observed spatial correlation of the emission with various tracers of cool gas in some of the galaxies. However, alternative scenarios, such as the resonance scattering by the plasma and the relic photo‐ionization by AGNs in the recent past, cannot be ruled out, at least in some cases, and are being examined. Such X‐ray spectroscopic studies are important to the understanding of the relationship of the emission to various high‐energy feedback processes in galaxies (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Near-field effects of Cherenkov radiation induced by ultra high energy cosmic neutrinos

The radio approach based on the Askaryan effect for detecting the ultra-high energy cosmic neutrinos has become a mature experimental technique. So far the existing calculations of the Cherenkov radiation associated with the Askaryan effect has been mostly based on the far-field approximation, whose validity maybe challenged when the detector is close to the event. In this paper we present an alternative approach to calculate the Cherenkov pulse by a numerical code based on the finite difference time-domain (FDTD) method. This approach has the advantage of providing the solution everywhere in space, contrary to other methods that rely on the far-field approximation. We also present a one-dimensional theoretical model for the shower with analytical solution, which helps to elucidate our nonzero-width simulation results. We show that for a shower with symmetric longitudinal development, the resulting near-field waveform would be asymmetric in time. In addition, we demonstrate that for a shower elongated by the LPM (Landau-Pomeranchuk-Migdal) effect and thus with a multi-peak structure, a bipolar, asymmetric waveform is still preserved in the near-field regime irrespective of the specific variations of the multi-peak structure, which makes it a generic, distinctive feature. This should provide an important characteristic signature for the identification of ultra-high energy cosmogenic neutrinos.     

Splash detachment of sand particles under varying contact stress field of wind-driven raindrop impact

The effects of wind-driven rain (WDR) on sand detachment were studied under various raindrop obliquities. Results suggested a significant reduction in compressive stress on sand surfaces for a two-dimensional experimental set-up in a wind tunnel. During experiments, sand particles in splash cups were exposed to both wind-free rain (WFR) and WDR driven by horizontal winds of 6.4, 8.9 and 12.8 m s⁻¹ and rainfall intensities of 50, 60, 75 and 90-mm h⁻¹ to assess the sand detachment rate (D, in g m⁻² s⁻¹). The effects of sand moisture state (dry and wet) on the detachment of different-sized particles (0.20–0.50 and 0.50–2.00 mm, respectively) were also tested. Factorial analysis of variance showed that shear and compressive stress components evaluated by horizontal and vertical kinetic energy flux terms (KE_x and KE_y, respectively, in J m⁻² s⁻¹) along with their vector sum (KE_r, in J m⁻² s⁻¹) explained the variation in D. Neither sand size nor sand moisture was statistically significant alone although binary interactions of KE_r, KE_x and KE_y with the sand size and three-way interaction of KE_x, sand size and moisture were statistically significant. These results can be explained by size-dependent variation in sand compressibility and surface friction related to the total stress field developed by a given partition of shear and compressive stresses of wind-driven oblique raindrops (KE_x/KE_y). Further analysis of the variation of the unit sand detachment rate (D_u = D/KE_r = g J⁻¹) with rain inclination (α, in degrees) better revealed the effect of WDR obliquity on D_u that further changed with sand size class and moisture state. Finally, the difference in the resulting stress field differentiable by the oblique raindrop trajectories of the experiment over sand surface significantly affected the non-cohesive particle detachment rates, to some extent interacted with size-dependent compressibility and interface shear strength of sand grains.