Stress accumulation and release reflected by acoustic emissions (AEs) during shearing of granular materials provide important information on failure mechanisms in seismic faults and landslides ...controlled by stick‐slip. Among many characteristics (amplitude, energy, counts, and frequency) of AE signals generated by stick‐slip, stress changes corresponding to various frequency AEs in different stages of the stick‐slip process are not clear, which limits our knowledge of the characteristics of precursory signals before stick‐slip failure. To better understand the physical mechanisms of granular stick‐slip, we monitored the mechanical and AE signals using high‐frequency (2 MHz) synchronous acquisition during constant‐speed shear of packs of uniform glass beads with different sizes at different normal stresses. The release rate of AE energy was found to accelerate with the dilatation of the sample volume, and the stress drop of stick‐slip was augmented with the increase of normal stress and particle size. Three characteristic events of single cycle stick‐slip were observed in this study: main slip, minor slip, and microslip. We analyzed the AE frequency spectra of these three event types. Both main slip and minor slip corresponded to stress drop and generated high‐frequency AEs (about several hundred kHz), while the AE frequencies generated by microslip were lower (about tens of kHz) and exhibited stress strengthening, which were not apparent in previous studies due to the low frequency of acquisition. We propose that the microslip is mainly due to sliding on grain contacts, while the main slip and minor slip resulted from breakage and reforming of force chains. Low‐frequency AEs from microslip may suggest a crucial precursor of seismic faults and landslides.
Plain Language Summary
The occurrence of earthquakes of similar magnitude (quasi‐periodic earthquakes) in a fault zone every few decades is thought to be controlled by stick‐slip of fault gouges. The mechanical evolution of fault gouges prior to earthquake occurrence is extremely complex and difficult to predict. However, many studies have observed the presence of significant microslip prior to stick‐slip failure of seismic faults, which may provide precursor information for an impending earthquake. Laboratory study of stick‐slip nucleation and failure mechanisms in granular materials provides important understanding of the physical mechanisms of quasi‐periodic earthquakes. Our experimental results of high‐frequency acoustic emission (AE) and ring‐shear simultaneous acquisition showed that stick‐slip failure (corresponding to the occurrence of an earthquake) leads to a decrease in the shear resistance of a granular system, generating high‐frequency acoustic signals. Increments of microslip increased the shear resistance of the granular system, and were recorded as low‐frequency acoustic signals before failure occurred. We suggest that the stick‐slip nucleation and failure were controlled by grain friction and collision, respectively. The different AE frequencies of the two may shed light on the precursor monitoring of quasi‐periodic earthquakes.
Key Points
Stick‐slip failure was associated with high‐frequency (∼105 Hz) acoustic emissions (AEs) and micro‐slip during stick‐slip nucleation was associated with low‐frequency (∼104 Hz) AEs
High‐frequency AEs may be caused by particle collisions after force‐chain breakage
Low‐frequency AEs may be caused by particle friction during force‐chain adjustment and may suggest important precursors of laboratory earthquakes
Desertification in Qinghai-Xizang (Tibet) Plateau is part of Chinese desertification. In the past decades, due to the climate warming, the climate condition in Qinghai-Xizang (Tibet) Plateau has been ...relatively dry. This has resulted in permafrost degradation and other environmental problems. In addition, the vegetation and the soil layer were also destroyed by unreasonable economic activities. Cultivated and grassland lands have become deserted. Nowadays, the desertification is still expending. In this paper, the factors affecting the desertification in Qinghai-Xizang (Tibet) Plateau were examined, and the desertification as well as its relationship with permafrost degradation was also discussed.
Determining the shear‐velocity dependence of dry granular friction can provide insight into the controlling variables in a dry granular friction law. Some laboratories believe that the quality of ...this study is at the forefront of the discipline for the following reasons. Results suggest that granular friction is greatly affected by shear‐velocity (v), but shear experiments over the large range of naturally occurring shear‐velocities are lacking. Herein we examined the shear velocity dependence of dry friction for three granular materials, quartz sand, glass beads and fluorspar, across nine orders of magnitude of shear velocity (10−8–2 m/s). Within this range, granular friction exhibited four regimes, following a broad approximate “m” shape including two velocity‐strengthening and two velocity‐weakening regimes. We discuss the possible physical mechanisms of each regime. This shear velocity dependence appeared to be universal for all particle types, shapes, sizes, and for all normal stresses over the tested range. We also found that ultra‐high frequency vibration as grain surfaces were scoured by micro‐chips were formed by spalling at high shear velocities, creating ∼20 μm diameter impact pits on particle surfaces. This study provides laboratory laws of a friction‐velocity (μ‐v) model for granular materials.
Plain Language Summary
Numerous phenomena of earth science can be simplified to shearing granular systems, such as landslide gouge and rock avalanches. It is believed that friction varies with shear velocity, and this is no exception for dry granular materials. Studying the law of friction variation over as large a range of velocity changes as possible aids in establishing a full life‐cycle hypothesis for landslides from initiation, through movement to cessation. We sheared granular materials across nine orders of magnitude, from 10−8 to 2 m/s and obtained an “M” shape law for the variation of friction with velocity. By analyzing the acoustic frequency of shear experiments at different velocities, we discovered that the acoustic frequency increased with shear velocity. By comparing the microscopic morphology of the particle surface before and after high‐velocity shearing, we hypothesized that the impact pits may be left by particle collisions during high‐velocity shearing. We proposed that the role of ultra‐high frequency vibration on high‐velocity shear weakening should be considered, which provides a basis for accurately revealing the physical mechanism of granular friction variation with velocity.
Key Points
This paper examines the shear velocity dependence of friction for dry granular materials, across nine orders of magnitude in shear velocity (10−8–2 m/s)
An “M‐shaped” law for the variation of friction with velocity is obtained including two velocity‐strengthening and two velocity‐weakening laws
There is microscopic evidence that ultra‐high frequency vibration may cause high velocity shear weakening
Brassinosteroids (BRs) are phytosteroid hormones controlling various physiological processes critical for normal growth and development. BRs are perceived by a protein complex containing two ...transmembrane receptor kinases, BRASSINOSTEROID INSENSITIVE 1 (BRI1) and BRI1-ASSOCIATED RECEPTOR KINASE 1 (BAK1) 1–3. BRI1 null mutants exhibit a dwarfed stature with epinastic leaves, delayed senescence, reduced male fertility, and altered light responses. BAK1 null mutants, however, only show a subtle phenotype, suggesting that functionally redundant proteins might be present in the Arabidopsis genome. Here we report that BAK1-LIKE 1 (BKK1) functions redundantly with BAK1 in regulating BR signaling. Surprisingly, rather than the expected bri1-like phenotype, bak1 bkk1 double mutants exhibit a seedling-lethality phenotype due to constitutive defense-gene expression, callose deposition, reactive oxygen species (ROS) accumulation, and spontaneous cell death even under sterile growing conditions. Our detailed analyses demonstrate that BAK1 and BKK1 have dual physiological roles: positively regulating a BR-dependent plant growth pathway, and negatively regulating a BR-independent cell-death pathway. Both BR signaling and developmentally controlled cell death are critical to optimal plant growth and development, but the mechanisms regulating early events in these pathways are poorly understood. This study provides novel insights into the initiation and crosstalk of the two signaling cascades.
Measurements were made in Black-boned (
n
= 40) and normal (
n
= 23) sheep (
Ovis aries
) from a flock in Nanping County of Yunnan Province, China, as well as a group (
n
= 21) of Romney Marsh ...sheep (
O. aries
) with the view to explaining the basis of the dark pigmentation occurring in the Black-boned animals. Plasma colour was significantly darker (
P
< 0.01) in Black-boned sheep than in their normal flock mates, which in turn had significantly darker plasma (
P
< 0.01) than the Romney Marsh sheep. Similar significant (
P
< 0.01) differences were measured for plasma tyrosinase activity and both groups of sheep from Nanping County had similar plasma concentrations of glutathione which were significantly smaller (
P
< 0.01) than for the Romney Marsh sheep.
A partial fragment of 750 bp of exon 1 of the gene encoding tyrosinase was constructed and found to contain two silent mutation sites (G192C and C462T) but there was no effect on amino acid sequences of
tyrosinase
. Using restriction fragment length polymorphism analyses two allelic variants of site G192C were identified giving rise to the genotypes GG, GC and CC; the frequencies of allele G being 0.914, 0.824 and 0.286 in the Black-boned sheep, their flock mates and the Romney Marsh sheep respectively. Plasma tyrosinase activity was similar for genotypes GG and GC and for both genotypes significantly higher (
P
< 0.05) than for genotype CC. The sheep from Nanping County displayed only the GG and GC genotypes and had predominantly black or black and white coat colour whereas the Romney Marsh sheep were of either genotype GC or CC and exhibited only white coat colouration. It is not appears that the dark pigmentation of the Black-boned sheep arises because of polymorphisms in the exon 1 of tyrosinase gene. However, this result could explain the differences between Black-boned and Romney Marsh sheep but not for differences between Black-boned and Nanping Normal sheep. Moreover, this result has provided evidence of genetic markers in the form of polymorphisms of the tyrosinase gene which may help to find the black traits causing mutations. There would be merit in further studies using histochemical and molecular techniques to elucidate the causes of the dark pigmentation in these Black-boned sheep.
A method based on the orthotropic elastic finite element analysis (FEA) has been presented to analyze the fatigue life of cooled turbine blades made of nickel-based single crystal superalloy (SC). ...Special attention was put on the influence of the crystallographic orientations on the strength and fatigue life of SC cooled turbine blades. It is shown that, due to the influence of the temperature distribution and complexity of cooling tunnel, the place of the maximum resolved shear stress in the blade is not corresponding to the most dangerous place, where results in the minimum fatigue life. For the SC cooled turbine blades studied in the paper, as the same of the most commercial SC blades in the world market, the axial direction is cast to 0
0
1 crystallographic orientation within 15° deviation, and the other two directions are in random. It is found that the randomness of the two directions has only limited influence on the distributions of Mises stress and the maximum resolved shear stress in the blade. But the deviation of the axial direction of the blade has obvious influence on the stress distribution, and the influence of the deviation and randomness orientations on the fatigue life is also obvious. Finally, the benefit of the optimization of the crystallographic orientations of SC cooled turbine blades on the fatigue life is highlighted.
Lung cancer is the most common malignant tumor worldwide. About 90% of lung cancers are considered non-small cell lung cancer (NSCLC). Ganoderan (GDN) is one of the components of
polysaccharides. ...Ganoderan A (GDNA), Ganoderan B (GDNB) and Ganoderan C (GDNC) were three polysaccharides isolated from the
fruiting body.
Cell growth was measured by Cell Counting kit-8 and colony formation assay, while cell motility was measured by transwell assay and wound healing assay. Apoptosis was measured by flow cytometry analysis and TUNEL staining, and protein expression was detected by Western blotting and immunohistochemistry.
Previous studies have shown that GDNB has the effects of hyperglycemic and kidney protection. However, the role of GDNB in tumors is currently unknown. This study elaborated the role of GDNB in NSCLC and its underlying molecular mechanisms. The results exerted that GDNB inhibited the growth of H510A and A549 cells by suppressing the expression of ki67 and PCNA. Besides, transwell assay and wound healing assay showed that GDNB inhibited invasion and migration of H510A and A549 cells in a concentration-dependent manner. Moreover, Western blotting also showed that GDNB downregulated the levels of N-cadherin, vimentin and Snail in H510A and A549 cells in a dose-dependent manner, while it upregulated the level of E-cadherin. Additionally, GDNB also promoted apoptosis of H510A and A549 cells by regulating the expression of Bcl-2, Bax, cleaved caspase 3 and cleaved PARP. Animal experiments revealed that GDNB inhibited tumor growth and metastasis, and induced apoptosis of tumor cells in vivo. Mechanically, GDNB suppressed the expression of Ras and c-Myc, and decreased the phosphorylation levels of MEK1/2 and ERK1/2.
Collectively, all data suggest that GDNB regulates the growth, motility and apoptosis of non-small cell lung cancer cells through ERK signaling pathway in vitro and in vivo.
•Tree-ring δ18O network indicates an east–west clustering pattern.•Regional variability of tree-ring δ18O is regulated by hydroclimatic changes.•Different patterns of tree-ring δ18O variability ...represent different moisture signals.•El Niño-Southern Oscillation modulates δ18Otree variability across southern China.
The East Asian summer monsoon (EASM) and Indian summer monsoon (ISM) are two interactive climate systems dominating the moisture variability of Monsoon Asia. However, ISM-EASM interactions and their effects on regional moisture dynamics remain unclear. This study investigated the spatiotemporal characteristics of monsoon-related hydroclimate variability by establishing a new tree-ring oxygen isotope ratio (δ18Otree) network of eight δ18Otree records covering the last 150 years in southern China, which differs from previous studies that used data from individual sites. The δ18Otree chronologies were found to be sensitive to regional hydroclimatic changes during the monsoon season. The δ18Otree network indicated an east–west clustering pattern in the ISM-EASM transitional zone, which demonstrates an asynchrony in δ18Otree variability in the west and east of this region. Regional variability of the west and east δ18Otree modes reflected the different moisture signals, as indicated by their significant correlations with modern observations and paleo-δ18O records in disparate upstream regions of moisture transport (the Indochina Peninsula and Southeast China). This finding was confirmed by the east–west distinct pattern of spatial isotopic depletion of monsoon rainfall that originates from coastal areas of tropical oceans (Bay of Bengal and South China Sea) to the study area, as well as the consistent present-day pattern of atmospheric vapor transport during the monsoon season. In addition, the west and east modes exhibited stronger associations with ISM variability, whereas the east–west δ18Otree gradient captured the EASM-related hydroclimatic signal, suggesting that summer moisture variability in the ISM-EASM transitional zone was regulated more by ISM than by EASM during the last 150 years. The relationships between δ18Otree and large-scale ocean–atmosphere interaction modes revealed that the El Niño-Southern Oscillation (ENSO) dominantly modulates δ18Otree variability across southern China.
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