Breaking down chipping and fragmentation in sediment transport: the control of material strength

As rocks are transported, they primarily undergo two breakdown mechanisms: fragmentation and chipping. Fragmentation is catastrophic breakup by fracture in the bulk – either by subcritical crack growth under repeated collisions, or from a single high-energy (supercritical) collision – and produces angular shards. Chipping is a distinct low-energy mechanism of impact attrition that involves shallow cracking; this process rounds river pebbles in a universal manner under bed-load transport. Despite its geophysical significance, the transition from chipping to fragmentation is not well studied. Here, we examine this transition experimentally by measuring the shape and mass evolution of concrete particles of varying strength, subject to repeated collisions in a rotating drum. For sufficiently strong particles, chipping occurred and was characterized by the following: attrition products were orders of magnitude smaller than the parent; attrition rate was insensitive to material strength; and particles experienced monotonic rounding toward a spherical shape. As strength decreased, we observed the onset of a subcritical cracking regime associated with fragmentation: mass of attrition products became larger and more varied; attrition rate was inversely proportional to material strength; and shape evolution fluctuated and became non-monotonic. Our results validate conceptual and numerical models for impact attrition: chipping follows “Sternberg's law” of exponential mass loss through time; for fragmentation, the lifetime of particles increases nonlinearly with material strength, consistent with “Basquin's law” of fatigue failure. We suggest that bedrock erosion models must be clarified to incorporate distinct attrition mechanisms, and that pebble or bedrock-channel shape may be utilized to deduce the operative mechanism in a given environment.

Multi-context genetic modeling of transcriptional regulation resolves novel disease loci

A majority of the variants identified in genome-wide association studies fall in non-coding regions of the genome, indicating their mechanism of impact is mediated via gene expression. Leveraging this hypothesis, transcriptome-wide association studies (TWAS) have assisted in both the interpretation and discovery of additional genes associated with complex traits. However, existing methods for conducting TWAS do not take full advantage of the intra-individual correlation inherently present in multi-context expression studies and do not properly adjust for multiple testing across contexts. We developed CONTENT---a computationally efficient method with proper cross-context false discovery correction that leverages correlation structure across contexts to improve power and generate context-specific and context-shared components of expression. We applied CONTENT to bulk multi-tissue and single-cell RNA-seq data sets and show that CONTENT leads to a 42% (bulk) and 110% (single cell) increase in the number of genetically predicted genes relative to previous approaches. Interestingly, we find the context-specific component of expression comprises 30\% of heritability in tissue-level bulk data and 75% in single-cell data, consistent with cell type heterogeneity in bulk tissue. In the context of TWAS, CONTENT increased the number of gene-phenotype associations discovered by over 47% relative to previous methods across 22 complex traits.

AI on Drugs: Can Artificial Intelligence Accelerate Drug Development? Evidence from a Large-Scale Examination of Bio-Pharma Firms

Advances in artificial intelligence (AI) could potentially reduce the complexities and costs in drug discovery. We conceptualize an AI innovation capability that gauges a firm’s ability to develop, manage, and utilize AI resources for innovation. Using patents and job postings to measure AI innovation capability, we find that it can affect a firm’s discovery of new drug-target pairs for preclinical studies. The effect is particularly pronounced for developing new drugs whose mechanism of impact on a disease is known and for drugs at the medium level of chemical novelty. However, AI is less helpful in developing drugs when there is no existing therapy. AI is also less helpful for drugs that are either entirely novel or those that are incremental “follow-on” drugs. Examining AI skills, a key component of AI innovation capability, we find that the main effect of AI innovation capability comes from employees possessing the combination of AI skills and domain expertise in drug discovery as opposed to employees possessing AI skills only. Having the combination is key because developing and improving AI tools is an iterative process requiring synthesizing inputs from both AI and domain experts during both the development and the operational stages of the tool. Taken together, our study sheds light on both the advantages and the limitations of using AI in drug discovery and how to effectively manage AI resources for drug development.

Controls on the rates and products of particle attrition by bed-load collisions

River rocks round through the process of impact attrition, whereby energetic collisions during bed-load transport induce chipping of the grain surface. This process is also important for bedrock erosion. Although previous work has shown that impact energy, lithology, and shape are controlling factors for attrition rates, the functional dependence among these quantities is not settled. Here we examine these factors using a double-pendulum apparatus that generates controlled collisions between two grains under conditions relevant for bed-load transport. We also determine the grain size distributions (GSDs) of the attrition products. Two experimental results appear to support previous treatments of impact erosion as brittle fracture: (i) mass loss is proportional to kinetic energy, and this proportionality is a function of previously identified material properties; and (ii) attrition-product GSDs are well described by a Weibull distribution. Chipping results from the development of shallow and surface-parallel cracks, a process that is distinct from bulk fragmentation that occurs at higher energies. We suggest that Hertzian fracture is the dominant mechanism of impact attrition for bed-load transport. We also identify an initial phase of rapid mass loss in which attrition is independent of energy and material properties; this is a shape effect associated with removal of very sharp corners. The apparent universality of both mass loss curves and attrition-product GSDs requires further investigation. Nonetheless, these findings are useful for interpreting the contribution of in-stream attrition to downstream fining and the production of sand resulting from bed-load transport of river pebbles.

The role of the factors determining national character in building civil society

The article deals with the mechanism of impact of sociopsychological phenomena such as the national character and the political mentality in the construction and functioning of civil society. It aims to show the impact of climate, religion, and the perception of happiness on the state of civil society through details of a national nature. The main research method is to compare data from global research on the state of civil society with data from climatic conditions, dominant religions, and happiness indices. The article proves coincidently that these factors are reflected in such essential characteristics of civil society as "openness" and "closed-mindedness". The interaction between the national character and the construction of civil society has two stages. It is concluded that the results obtained are important to evaluate the prospects for the construction and development of civil society in different countries and regions of the world. Further research in this direction involves the study of other aspects of the impact of national character and political mindset on the functioning of civil society.

Impact-Induced Liquefaction Mechanism of Sandy Silt at Different Saturations

Landslide-induced liquefaction has received extensive attention from scholars in recent years. In the study of loess landslides in the southern Loess Plateau of Jingyang, some scholars have noted the liquefaction of the near-saturated sandy silt layer that is caused by the impact of loess landslides on the erodible terrace. The impact-induced liquefaction triggered by landslides is probably the reason for the long-runout landslides on the near-horizontal terrace. In order to reveal the mechanism of impact-induced liquefaction, this paper investigates the development of pore pressure and the impact-induced liquefaction of sandy silt under the influence of saturation through laboratory experiments, moisture content tests, and vane shear tests. It has been found that both the total pressure and pore water pressure undergo a transient increase and decrease at the moment of impact on the soil, which takes 40–60 ms to complete and only about 20 ms to arrive at the peak. Moreover, silty sand with a saturation of more than 80° was liquefied under the impact, and the liquefaction occurred in the shallow layer of the soil body. The shear strength of the liquefied part of the soil is reduced to 1.7∼2.8 kPa. Soils with lower saturation did not liquefy. The mechanism of the impact-induced liquefaction can be described as follows: under impact, the water in the soil gradually fills the pores of the soil body as the pore size decreases, and when the contact between the soil particles is completely replaced by pore water, the soil body loses its shear strength and reaches a liquefied state. Soils in the liquefied state have a very high permeability coefficient, and the water inside the soil body migrates upward as the particles settle, resulting in high-moisture content in the upper soil.

FDI, Spillover Effect and Green Total Factor Productivity (GTFP) - Research from the Perspective of Regional Heterogeneity

The report of the 19th National Congress of the Communist Party of China emphasized the need to promote green development and strengthen the environmental protection system. China’s introduction of foreign investment has gradually shifted from emphasis on “quantity” to “quality” in the context of the new normal. In view of this, this paper discussed the mechanism of impact of FDI on China’s regional GTFP with the relationship between FDI and the regional GTFP as the logic starting point. The research results show that FDI has in general exerted a “pollution halo” effect in China, which affects the regional GTFP through technology and human capital spillover effects; FDI has non-linear impact on GTFP at different levels of environmental regulation and marketization; “pollution haven", “bottom line competition” and other phenomena will occur at low levels of environmental regulation and marketization; FDI will inhibit the increase in China’s regional GTFP; the impact of FDI on GTFP is regionally different, and the western and northeastern regions are “pollution havens” in China.

A Study on the Mechanism of Impact between Curved Bridge Segments Using Nonsmooth Dynamics

It has been observed in many previous earthquakes that impact often occurs between the main girders in curved bridges. An earthquake can result in deck-unseating leading to catastrophic destruction of the structure. In this paper, the nonsmooth multirigid body dynamics method and the set-valued formulation were used to model and analyze the mechanism of impact between the curved bridge segments. The analysis demonstrated that these impacts are the major cause of segment rotation. The main contribution of this paper is to use Newton’s impact law and Coulomb’s friction law to describe the interaction between the curved bridge segments in the form of a set-valued function and to express impacts with friction as a linear complementary problem. For frictionless and frictional contact, the paper considers the single-point and multipoint impacts using the linear complementary formula to detect the unique actual slip-stick conditions of these states. A variety of criteria for distinguishing each case are presented and the results provide the kinetic characteristics of each contact case. The analysis has shown that the impact between the segments of a curved bridge and the tendency of the segments to rotate (and thus detach) are related to the overall geometry, the coefficient of restitution, the coefficient of friction, and the preimpact conditions in the plane of motion. Finally, a theoretical relationship diagram of the impact, rotation slip, and stick condition of the curved bridge segments at the contact point is given. The presented results will be useful for the seismic design of curved bridges.