► The challenge of rockburst risk control and mitigation is discussed. ► It emphasizes that effective rock support is the final line of defense to ensure mine safety. ► Seven principles for guiding ...rock support design in burst-prone grounds are presented. ► These principles help to master the art of rock support in burst-probe grounds.
Rock support in burst-prone ground requires a good understanding of rock mass behavior under high stress conditions and the behavior and functionality of each rock support element as well as the behavior of the rock support system. Seven principles which can lead to making the right judgment and decision with regards to rock support design in burst-prone ground are presented in this paper. A good understanding of these principles helps ground control engineers to master the art of rock support in burst-probe grounds so as to develop useful methodology for design.
Quantum phase transitions (QPTs) are usually associated with many-body systems in the thermodynamic limit when their ground states show abrupt changes at zero temperature with variation of a ...parameter in the Hamiltonian. Recently it has been realized that a QPT can also occur in a system composed of only a two-level atom and a single-mode bosonic field, described by the quantum Rabi model (QRM). Here we report an experimental demonstration of a QPT in the QRM using a
Yb
ion in a Paul trap. We measure the spin-up state population and the average phonon number of the ion as two order parameters and observe clear evidence of the phase transition via adiabatic tuning of the coupling between the ion and its spatial motion. An experimental probe of the phase transition in a fundamental quantum optics model without imposing the thermodynamic limit opens up a window for controlled study of QPTs and quantum critical phenomena.
By applying the Griffith stress criterion of brittle failure, one can find that the uniaxial compressive strength (s(c)) of rocks is eight times the value of the uniaxial tensile strength (s(t)). The ...Griffith strength ratio is smaller than what is normally measured for rocks, even with the consideration of crack closure. The reason is that Griffith's theories address only the initiation of failure. Under tensile conditions, the crack propagation is unstable so that the tensile crack propagation stress (s(cd))(t) and the peak tensile strength s(t) are almost identical to the tensile crack initiation stress (s(ci))(t). On the other hand, the crack growth after crack initiation is stable under a predominantly compressive condition. Additional loading is required in compression to bring the stress from the crack initiation stress s(ci) to the peak strength s(c). It is proposed to estimate the tensile strength of strong brittle rocks from the strength ratio of $$ R = {\frac{{\sigma_{\text{c}} }}{{\left
The epithelial-mesenchymal transition (EMT) is crucial to cancer progression and metastasis. Although multiple cellular miRNAs have been identified to regulate the EMT and metastasis in cancers, the ...role of viral miRNAs in cancer progression remains largely unknown. Nasopharyngeal carcinoma (NPC) is an Epstein-Barr virus (EBV)-associated malignancy typically characterized by its early metastasis. In the present study, we have discovered the involvement of a viral miRNA, EBV-miR-BART7-3p, in the EMT and metastasis of NPC cells. Initially, we observed that EBV-miR-BART7-3p was highly expressed in NPC and positively correlated with lymph node metastasis and clinical stage of NPC. Subsequently, we demonstrated that EBV-miR-BART7-3p enhanced cell migration/invasion in vitro, cancer metastasis in vivo, and particularly the EMT characterized by loss of epithelial markers and gain of mesenchymal features in NPC cells. Furthermore, mechanistic studies disclosed that EBV-miR-BART7-3p targeted a major human tumor suppressor PTEN, modulating PI3K/Akt/GSK-3β signaling and eventually leading to the high expression and nuclear accumulation of Snail and β-catenin, which favor EMT. Knockdown of PTEN could phenocopy the effect of EBV-miR-BART7-3p, whereas re-expression of PTEN resulted in a phenotypic reversion. Moreover, these findings were supported by an observation of an EBV-positive cell model in which silencing of endogenous EBV-miR-BART7-3p partially attenuated cell migration/invasion and altered EMT protein expression pattern via reverting PI3K/Akt, Snail and β-catenin expression. Thus, this study suggests a novel mechanism by which EBV-miR-BART7-3p modulates the EMT and metastasis of NPC cells, and a clinical implication of EBV-miR-BART7-3p as a potential biomarker or therapeutic target.
Rock support in strainburst-prone ground Cai, M.
International journal of mining science and technology,
July 2019, 2019-07-00, 2019-07-01, Letnik:
29, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Strainburst is the most frequently encountered type of rockburst in underground mines. Strainburst occurs when the stress near the excavation boundary reaches the peak strength of the rock mass ...causing it to fail suddenly and violently. To mitigate strainburst damage risk, effective rock support is needed. In strainburst-prone grounds, it is critical to have rock support components to fulfill the role of rock reinforcement first to prevent rock failure. On the other hand, well-retained and reinforced rock masses may be excessively deformed and fail violently. In such a case, yielding elements are needed in the rock support system to absorb the excess strain energy released due to rock failure. The conventional method to support strainburst-prone grounds is to install rock reinforcement system using rebar and mesh first and then install yielding support system using dynamic rockbolts at a later stage. This two-stage rock support installation process is not effective because it can adversely impact mine production schedule. This paper presents a new, patented dynamic rockbolt, which is called superbolt and is developed for rock support in burst-prone grounds. Laboratory testing confirmed that the superbolt has superb capacity to achieve the goal of reinforcing and holding rock masses. The superbolt is characterized by high dynamic energy absorption capacity, consistent performance, and the ability to withstand repeated dynamic loading. The new rockbolt can be used in a one-pass rock support system to facilitate rapid drift development in underground mines and increase mine safety and productivity.
By applying the Griffith stress criterion of brittle failure, one can find that the uniaxial compressive strength (σ
c
) of rocks is eight times the value of the uniaxial tensile strength (σ
t
). The ...Griffith strength ratio is smaller than what is normally measured for rocks, even with the consideration of crack closure. The reason is that Griffith’s theories address only the initiation of failure. Under tensile conditions, the crack propagation is unstable so that the tensile crack propagation stress (σ
cd
)
t
and the peak tensile strength σ
t
are almost identical to the tensile crack initiation stress (σ
ci
)
t
. On the other hand, the crack growth after crack initiation is stable under a predominantly compressive condition. Additional loading is required in compression to bring the stress from the crack initiation stress σ
ci
to the peak strength σ
c
. It is proposed to estimate the tensile strength of strong brittle rocks from the strength ratio of
The term
accounts for the difference of crack growth or propagation in tension and compression in uniaxial compression tests.
depends on rock heterogeneity and is larger for coarse grained rocks than for fine grained rocks. σ
ci
can be obtained from volumetric strain measurement or acoustic emission (AE) monitoring. With the strength ratio
R
determined, the tensile strength can be indirectly obtained from
It is found that the predicted tensile strengths using this method are in good agreement with test data. Finally, a practical estimate of the Hoek–Brown strength parameter
m
i
is presented and a bi-segmental or multi-segmental representation of the Hoek–Brown strength envelope is suggested for some brittle rocks. In this fashion, the rock strength parameters like σ
t
and
m
i
, which require specialty tests such as direct tensile (or Brazilian) and triaxial compression tests for their determination, can be reasonably estimated from uniaxial compression tests.
Geotechnical design input parameters, such as in situ stress field, rock mass strength parameters and deformation modulus, are never known precisely. There are always uncertainties involved in these ...parameters, some are intrinsic and others are due to lack of knowledge or understanding of these parameters. To quantify the effects of these uncertainties on tunnel and cavern design, it is necessary to utilize probabilistic analysis methods. In the present study, a quantitative, probabilistic approach to use the Geological Strength Index (GSI) system for rock mass characterization is presented. It employs the block volume and a joint condition factor as quantitative characterization factors to determine the GSI values. The approach is built on the linkage between descriptive geological terms and measurable field parameters such as joint spacing and joint roughness, which are random variables. Using GSI values obtained from field mapping data, and in combination with the intact rock strength properties, the probability density distributions of rock mass strength parameters and elastic moduli of the jointed rock mass can be calculated using Monte Carlo method. Furthermore, probabilistic analysis of tunnel and cavern stability based on the variable input parameters is conducted employing the point estimate method. One example is given to illustrate how to consider the variability of in situ stress and the rock mass properties in tunnel and cavern design. The method presents an approach for systematic assessment of uncertainty in rock mass characterization in rock engineering, and it can assist us to better understand how uncertainty arises and how the rock support system design decision may be affected by it.
Nanometer-sized diamonds containing nitrogen-vacancy defect centers (NV) are promising nanosensors in biological environments due to their biocompatibility, bright fluorescence, and high magnetic ...sensitivity at ambient conditions. Here we report on the detection of ferritin molecules using magnetic noise induced by the inner paramagnetic iron as a contrast mechanism. We observe a significant reduction of both coherence and relaxation time due to the presence of ferritin on the surface of nanodiamonds. Our theoretical model is in excellent agreement with the experimental data and establishes this method as a novel sensing technology for proteins.
In the present study, fracture initiation and propagation from a pre-existing plane interface in a Brazilian disc is investigated using a finite-discrete element combined method. Different fracture ...patterns, depending on the frictional resistance of the pre-existing crack or interface, are observed from the numerical simulation. It is found that when there is no or very little frictional resistance on the surfaces of the pre-existing crack, the primary fractures (wing cracks), which are tensile in nature and are at roughly right angles to the pre-existing crack, start from the tips of the pre-existing crack. As the friction coefficient increases, the wing cracks’ initiation locations deviate from the crack tips and move toward the disc center. Secondary fractures, which are also tensile in nature, initiate from the disc boundary and occur only when the length of the pre-existing crack is sufficiently long. The secondary fractures are roughly sub-parallel to the pre-existing crack. The failure load is found to be influenced by the friction coefficient of the pre-existing crack. A 38 % failure load increase can result when the friction coefficient changes from 0 to 1. A good understanding of the fracture initiation and propagation in the forms of primary and secondary fractures provides insight into explaining some fracture patterns observed underground.
Gas flaring is a prominent source of VOCs, CO, CO2, SO2, PAH, NOX and soot (black carbon), all of which are important pollutants which interact, directly and indirectly, in the Earth’s climatic ...processes. Globally, over 130 billion cubic metres of gas are flared annually. We review the contribution of gas flaring to air pollution on local, regional and global scales, with special emphasis on black carbon (BC, “soot”). The temporal and spatial characteristics of gas flaring distinguishes it from mobile combustion sources (transport), while the open-flame nature of gas flaring distinguishes it from industrial point-sources; the high temperature, flame control, and spatial compactness distinguishes gas flaring from both biomass burning and domestic fuel-use. All of these distinguishing factors influence the quantity and characteristics of BC production from gas flaring, so that it is important to consider this source separately in emissions inventories and environmental field studies. Estimate of the yield of pollutants from gas flaring have, to date, paid little or no attention to the emission of BC with the assumption often being made that flaring produces a smokeless flame. In gas flares, soot yield is known to depend on a number of factors, and there is a need to develop emission estimates and modelling frameworks that take these factors into consideration. Hence, emission inventories, especially of the soot yield from gas flaring should give adequate consideration to the variation of fuel gas composition, and to combustion characteristics, which are strong determinants of the nature and quantity of pollutants emitted. The buoyant nature of gas flaring plume, often at temperatures in the range of 2000 K, coupled with the height of the stack enables some of the pollutants to escape further into the free troposphere aiding their long-range transport, which is often not well-captured by model studies.
•In-depth analysis of gas flaring and its attendant atmospheric emissions.•Critical review of literature on black carbon emissions from gas flaring.•Important gaps exist in the estimation of emissions from gas flaring.•Review justifies including gas flaring explicitly in inventories and global models.•A framework is proposed for the development of more robust emission factors.
The review identified gaps in the estimation of emissions from the gas flaring process and argues for explicit recognition of gas flaring emissions in emission inventories and global models.
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