Water effects on rock strength and stiffness degradation

Reduction in strength and stiffness in rocks attributed to an increase in water content has been extensively researched on a large variety of rock types over the past decades. Due to the considerable variations of texture and lithology, the extent of water-weakening effect is highly varied among different rock types, spanning from nearly negligible in quartzite to 90 % of uniaxial compressive strength reduction in shale. Readers, however, often face difficulties in comparing the data published in different sources due to the discrepancy of experimental procedures of obtaining the water saturation state and how the raw laboratory data is interpreted. In view of this, the present paper first reviews the terminologies commonly used to quantify the amount of water stored in rocks. The second part of the paper reviews the water-weakening effects on rock strengths, particularly focusing on uniaxial compressive strength and modulus, as well as tensile strength, under quasi-static loading and dynamic loading. The correlation relationships established among various parameters, including porosity, density and fabric of rocks, and external factors such as strain rate, surface tension and dielectric constant of the saturating liquid, absorption percentage and suction pressure, are reviewed and presented toward the end of the paper.     

Human control of climate change

The use of analogies and repeated feedback might help people learn about the dynamics of climate change. In this paper, we study the influence of repeated feedback on the control of a carbon-dioxide (CO₂) concentration to a goal level in a Dynamic Climate Change Simulator (DCCS) using the “bathtub” analogy. DCCS is a simplification of the complex climate system into its essential elements: CO₂ concentration (stock); man-made CO₂ emissions (inflow); and natural CO₂ removal or absorption in the atmosphere (outflow). In a laboratory experiment involving DCCS, we manipulated feedback delays in two ways: the frequency of emission decisions and the rate of CO₂ absorption from the atmosphere (climate dynamics). Our results revealed that participants’ ability to control the CO₂ concentration generally remained poor even in conditions where they were allowed to revise their emission decisions frequently (i.e., every 2?years) and where the climate dynamics were rapid (i.e., 1.6% of CO₂ concentration was removed every year). Participants’ control of the concentration only improved with repeated feedback in conditions of lesser feedback delay. Moreover, the delay due to climate dynamics had a greater effect on participants’ control than the delay due to emission decisions frequency. We provide future research directions and highlight the potential of using simulations like DCCS to help people learn about dynamics of Earth’s climate.     

Nonlinear radial oscillations of coronal loops

The behavior of radial oscillations of coronal magnetic tubes is considered in a weakly nonlinear approximation. The nonlinear Schrödinger equation, the coefficients of which are found from the tube and radial mode parameters, has been obtained for the oscillation amplitude. The coefficients have been calculated for the fundamental radial mode, which is characterized by the absence of the cutoff in the region of low frequencies. It has been shown that the modulation instability condition is satisfied in a wide range of mode parameter values, which indicates that large-amplitude radial oscillations can exist in coronal loops.