This paper explores the influence of the confining stress on rock fragmentation under the cutter of tunnel boring machine (TBM) by indentation test. Acoustic emission (AE) system was employed for ...real-time monitoring the rock fragmentation process during the indentation test. Granite and marble samples were used in the indentation test. The rock fragmentation processes with the different confining stress levels was studied based on the characteristics of force–penetration depth curve and the AE parameters, including AE energy rate, hit counts, amplitude and location of AE events. After the indentation test, the rock samples were cut along the centerline of rock samples and subsequently the crack distribution and the size of crushed zone were measured. The test results showed that the force for crack initiation and crushed zone size increased with increasing confining stress. The cracks tend to propagate to the free surface as the confining stress increases. But for the marble samples, there exists a critical confining stress condition, such that if the confining stress is more than the critical value, the force for crack initiation and crushed zone size decrease dramatically. Moreover, it was found that rock slabbing induced by confining stress had occurred before TBM cutter indentation. Such confining stress condition promotes rock fragmentation.
•Influence of confining stress on rock fragmentation by a TBM cutter is studied by indentation test.•AE technique is used for real-time monitoring rock fragmentation during indentation test.•The damage zone and crack distribution are observed by the cross-section of the failed samples.
The TBM tunneling process in hard rock is actually a rock or rock mass breakage process, which determines the efficiency of tunnel boring machine (TBM). On the basis of the rock breakage process, a ...rock mass conceptual model that identifies the effect of rock mass properties on TBM penetration rate is proposed. During the construction of T05 and T06 tunnels of DTSS project in Singapore, a comprehensive program was performed to obtain the relevant rock mass properties and TBM performance data. A database, including rock mass properties, TBM specifications and the corresponding TBM performance, was established. Combining the rock mass conceptual model for evaluating rock mass boreability with the established database, a statistical prediction model of TBM penetration rate is set up by performing a nonlinear regression analysis. The parametric studies of the new model showed that the rock uniaxial compressive strength and the volumetric joint count have predominantly effects on the penetration rate. These results showed good agreement with the numerical simulations. The model limitations were also discussed.
This Letter reports a measurement of the flux and energy spectrum of electron antineutrinos from six 2.9 GWth nuclear reactors with six detectors deployed in two near (effective baselines 512 and 561 ...m) and one far (1579 m) underground experimental halls in the Daya Bay experiment. Using 217 days of data, 296 721 and 41 589 inverse β decay (IBD) candidates were detected in the near and far halls, respectively. The measured IBD yield is (1.55±0.04) ×10(-18) cm(2) GW(-1) day(-1) or (5.92±0.14) ×10(-43) cm(2) fission(-1). This flux measurement is consistent with previous short-baseline reactor antineutrino experiments and is 0.946±0.022 (0.991±0.023) relative to the flux predicted with the Huber-Mueller (ILL-Vogel) fissile antineutrino model. The measured IBD positron energy spectrum deviates from both spectral predictions by more than 2σ over the full energy range with a local significance of up to ∼4σ between 4-6 MeV. A reactor antineutrino spectrum of IBD reactions is extracted from the measured positron energy spectrum for model-independent predictions.
Metamaterials open up various exotic means to control electromagnetic waves and among them polarization manipulations with metamaterials have attracted intense attention. As of today, static ...responses of resonators in metamaterials lead to a narrow-band and single-function operation. Extension of the working frequency relies on multilayer metamaterials or different unit cells, which hinder the development of ultra-compact optical systems. In this work, we demonstrate a switchable ultrathin terahertz quarter-wave plate by hybridizing a phase change material, vanadium dioxide (VO2), with a metasurface. Before the phase transition, VO2 behaves as a semiconductor and the metasurface operates as a quarter-wave plate at 0.468 THz. After the transition to metal phase, the quarter-wave plate operates at 0.502 THz. At the corresponding operating frequencies, the metasurface converts a linearly polarized light into a circularly polarized light. This work reveals the feasibility to realize tunable/active and extremely low-profile polarization manipulation devices in the terahertz regime through the incorporation of such phase-change metasurfaces, enabling novel applications of ultrathin terahertz meta-devices.
MicroRNAs (miRNAs) deregulation is frequent in human gastric cancers (GCs), but the role of specific miRNAs involved in this disease remains elusive. MiR-22 was previously reported to act as tumor ...suppressors or oncogenes in diverse cancers. However, their accurate expression, function and mechanism in GC are largely unclear. Here, we found that the expression of miR-22 was significantly reduced in clinical GC tissues compared with paired adjacent normal tissues, and was significantly correlated with a more aggressive phenotype of GC in patients, and miR-22 low expression correlated with poor overall survival. The introduction of miR-22 markedly suppressed GC cell growth, migration and invasion, and inhibition of miR-22 promoted GC cell proliferation, migration and invasion in vitro. We further demonstrated that miR-22 acted as tumor suppressors through targeting extracellular matrix (ECM) remodeling member matrix metalloproteinase 14 (MMP14) and epithelial-to-mesenchymal transition (EMT) inducer Snail in GC. Moreover, ectopic expression of MMP14 or Snail restored inhibitory effects of miR-22 on cell migration and invasion in GC cells, and a negative relationship between the miR-22 expression and MMP14 or Snail mRNA levels was observed in GC. Finally, overexpression of miR-22 suppressed tumor growth, peritoneal dissemination and pulmonary metastasis in vivo. Taken together, we identified that miR-22 is a potent tumor suppressor in GC. MiR-22 downregulation promotes GC invasion and metastasis by upregulating MMP14 and Snail, and then inducing ECM remodeling and EMT. These findings provide a better understanding of the development and progression of GC and may be an important implication for future therapy of the GC.
The Daya Bay experiment has observed correlations between reactor core fuel evolution and changes in the reactor antineutrino flux and energy spectrum. Four antineutrino detectors in two experimental ...halls were used to identify 2.2 million inverse beta decays (IBDs) over 1230 days spanning multiple fuel cycles for each of six 2.9 GW_{th} reactor cores at the Daya Bay and Ling Ao nuclear power plants. Using detector data spanning effective ^{239}Pu fission fractions F_{239} from 0.25 to 0.35, Daya Bay measures an average IBD yield σover ¯_{f} of (5.90±0.13)×10^{-43} cm^{2}/fission and a fuel-dependent variation in the IBD yield, dσ_{f}/dF_{239}, of (-1.86±0.18)×10^{-43} cm^{2}/fission. This observation rejects the hypothesis of a constant antineutrino flux as a function of the ^{239}Pu fission fraction at 10 standard deviations. The variation in IBD yield is found to be energy dependent, rejecting the hypothesis of a constant antineutrino energy spectrum at 5.1 standard deviations. While measurements of the evolution in the IBD spectrum show general agreement with predictions from recent reactor models, the measured evolution in total IBD yield disagrees with recent predictions at 3.1σ. This discrepancy indicates that an overall deficit in the measured flux with respect to predictions does not result from equal fractional deficits from the primary fission isotopes ^{235}U, ^{239}Pu, ^{238}U, and ^{241}Pu. Based on measured IBD yield variations, yields of (6.17±0.17) and (4.27±0.26)×10^{-43} cm^{2}/fission have been determined for the two dominant fission parent isotopes ^{235}U and ^{239}Pu. A 7.8% discrepancy between the observed and predicted ^{235}U yields suggests that this isotope may be the primary contributor to the reactor antineutrino anomaly.
Two headrace tunnels and the drainage tunnel were excavated by tunnel boring machines (TBMs) in Jinping II Hydropower Station. During TBM excavation, two types of slabbing failure were encountered in ...these deep buried marble tunnels. One is rock bursting and the other is non-violent slabbing. In order to study the rock burst and slabbing failure, a unique true triaxial rock burst test was carried out to simulate the rock burst process with different in situ stresses. Four rock samples in different marble layers were obtained in the site, and then four experiments are conducted under the same stressed conditions as the in situ field. The rock burst process and slabbing failure phenomena of the four experiments are in good accordance with the observations of corresponding excavation site. The failure modes of slabbing and rock burst in different rock groups can be predicted based on the experiments. The influence of the slabbing and rock burst failure on TBM excavation is analyzed in depth. Non-violent slabbing is beneficial to the rock breakage process. Rock burst with violent slabbing process greatly affects the tunnel support, cutter and cutterhead damage, gripper movement and force and so on.
► Slabbing and rock burst are encountered in TBM excavated tunnels with high in situ stresses. ► True three axial experiments are carried out to simulate the rock burst process and mechanisms. ► The influence of slabbing and rock burst failure on TBM tunnelling is analyzed in depth. ► Non-violent slabbing increases TBM efficiency and rock burst greatly hinders the TBM advance.
Because the construction of dams and hydro-electric power stations of Liujiaxia and Yanguoxia across the Yellow River in West Gansu Province, North-West China, inhabitants in the reservoir areas were ...resettled in Heifangtai Loess Platform. Irrigation thus started in 1968. Perched water table was significantly raised and resulted in many loess flow failures in the past 30 years. This type of landslide was often featured by long runout distance, high speed and recurrence. Laboratory tests along ICU and CSD stress paths were performed. It is shown that the loess has a strong strain-softening behavior and instability can occur in drained condition before undrained liquefaction. The failure mechanism of loess flow can be interpreted as the following process: with increasing perched water table, collapse in loess was first triggered in drained condition and led to undrained loading to adjacent soil in the lower saturated part of the loess platform. Under gravity loading applied by upper dry loess, undrained flow failure mobilized, eventually.
A search for light sterile neutrino mixing was performed with the first 217 days of data from the Daya Bay Reactor Antineutrino Experiment. The experiment's unique configuration of multiple baselines ...from six 2.9 GW(th) nuclear reactors to six antineutrino detectors deployed in two near (effective baselines 512 m and 561 m) and one far (1579 m) underground experimental halls makes it possible to test for oscillations to a fourth (sterile) neutrino in the 10(-3) eV(2)<|Δm(41)(2) |< 0.3 eV(2) range. The relative spectral distortion due to the disappearance of electron antineutrinos was found to be consistent with that of the three-flavor oscillation model. The derived limits on sin(2) 2θ(14) cover the 10(-3) eV(2) ≲ |Δm(41)(2)| ≲ 0.1 eV(2) region, which was largely unexplored.
•Three sets of TBM penetration tests are conducted with different in situ stress conditions in three TBM tunnels.•The rock mass boreability index and the muck sieve test results are analyzed in the ...penetration tests.•The test results revealed the influence of in situ stress on rock mass boreability and TBM excavation process.•The influence degree of different in situ stresses for rock mass boreability is obtained.
Rock mass boreability is a comprehensive parameter reflecting the interaction between rock mass and a tunnel boring machine (TBM). Many factors including rock mass conditions, TBM specifications and operation parameters influence rock mass boreability. In situ stress, as one of the important properties of rock mass conditions, has not been studied specifically for rock mass boreability in TBM tunneling. In this study, three sets of TBM penetration tests are conducted with different in situ stress conditions in three TBM tunnels of the Jinping II Hydropower Station. The correlation between TBM operation parameters collected during the tests and the rock mass boreability index is analyzed to reveal the influence of in situ stress on rock mass boreability and TBM excavation process. The muck produced by each test step is collected and analyzed by the muck sieve test. The results show that in situ stress not only influences the rock mass boreability but also the rock fragmentation process under TBM cutters. If the in situ stress is high enough to cause the stress-induced failure at the tunnel face, it facilitates rock fragmentation by TBM cutters and the corresponding rock boreability index decreases. Otherwise, the in situ stress restrains rock fragmentation by TBM cutters and the rock mass boreablity index increases. Through comparison of the boreability index predicted by the Rock Mass Characteristics (RMC) prediction model with the boreability index calculated from the penetration test results, the influence degree of different in situ stresses for rock mass boreability is obtained.
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