Methodology for identifying the damage state of sandstone using Mel-frequency cepstral coefficient of acoustic emission

Rock mass structure rupture is an important factor that seriously restricts the construction and safe operation of underground space engineering projects such as mines, subways and tunnels. Realizing the identification of rock mass fracture state is one of the hotspots and emphases of current research. In this study, some experiments of sandstone loading failure under different conditions were carried out, the acoustic emission Mel-frequency cepstral coefficient (MFCC) and its fluctuation difference during the whole loading process were extracted, the variation law of the coefficient and its fluctuation difference during the whole loading failure process was studied, and the correlation characteristics of coefficient No.1 (According to the calculation of acoustic emission Mel-frequency cepstral coefficients, it can be seen that a set of acoustic emission Mel-frequency cepstral coefficient includes 12, and coefficient No.1 refers to the first Mel-frequency cepstral coefficient) and its fluctuation difference with the fracture state of sandstone were analyzed. Based on this, a method to identify sandstone fracture state using the Mel-frequency cepstral of acoustic emission was proposed, and the identification criteria was constructed. The identification effect was finally verified. The results show that with loading increase, the coefficient No.1 increases as a whole, and the coefficient value and its discreteness increase significantly in the failure stage and show significant regular fluctuations. The fluctuation difference of the coefficient has the characteristics of periodic variation. The size of the fluctuation difference and its fluctuation can characterize the fracture of sandstone. The overall increase and sudden increase of the fluctuation difference can reflect the macroscopic fracture of sandstone in the unstable deformation and post-peak failure stage, and the sudden increase level of the fluctuation difference can reflect the fracture degree of sandstone. The acoustic emission Mel-frequency cepstral coefficient and its fluctuation difference show good response characteristics to sandstone fracture, which is less affected by different loading conditions, thus they have applicability in reflecting sandstone fracture. The coefficient No.1 and its fluctuation difference have a good correlation with the fracture state of sandstone. The correlation can be divided into three stages as: in the micro-fracture stage of sandstone, the coefficient No.1 and its fluctuation difference are intensively distributed; in the unstable deformation stage just prior to the peak load, the distribution range increases sharply, the overall value increases and the high abnormal value appears; in the post-peak failure stage, the distribution range further increases, the overall value is higher, and more high abnormal values appear. The identification method and criteria of sandstone fracture state were constructed by using the 75% site value and outliers of coefficient No.1 and the 75% site value and outliers of the fluctuation difference of coefficient No.1. The effect of the identification criteria was tested by the confusion matrix of the three-classification model. The accuracy and precision of identification are 90.43% and 94.45%, respectively, which indicate the identification effect is good. The results can provide a reference for the identification of the fracture state of other types of coal and rocks, and for the monitoring and early warning of coal rock instability

Influence of the strong magnetocrystalline anisotropy on the magnetocaloric properties of MnP single crystal

Manganese monophosphate MnP single crystal deserves attention due to its rich magnetic phase diagram, which is quite different depending on the direction of the applied magnetic field. Generally speaking, it has a Curie temperature around 291 K and several other magnetic arrangements at low temperatures (cone-, screw-, fan-, and ferromagnetic-type structures). This richness is due to the strong magnetocrystalline anisotropy. In this sense, the present paper makes a thorough description of the influence of this anisotropy on the magnetocaloric properties of this material. From a fundamental view we could point out, among those several magnetic arrangements, the most stable one. On the other hand, from an applied view, we could show that the magnetic entropy change around room temperature ranges from -4.7 to -3.2 J/kg K, when the magnetic field (5T) is applied along the easy and hard magnetization directions, respectively. In addition, we have shown that it is also possible to take advantage of the magnetic anisotropy for magnetocaloric applications, i.e., we have found a quite flat magnetic entropy change (with a huge relative cooling power), at a fixed value of magnetic field, only rotating the crystal by 90 degrees.771

Recycled gabbro signature in hotspot magmas unveiled by plume–ridge interactions

Lavas erupted within plate interiors above upwelling mantle plumes have chemical signatures that are distinct from midocean ridge lavas. When a plume interacts with a mid-ocean ridge, the compositions of both their lavas changes, but there is no consensus as to how this interaction occurs1–3. For the past 15 Myr, the Pacific–Antarctic mid-ocean ridge has been approaching the Foundation hotspot4 and erupted lavas have formed seamounts. Here we analyse the noble gas isotope and trace element signature of lava samples collected from the seamounts. We find that both intraplate and on-axis lavas have noble gas isotope signatures consistent with the contribution from a primitive plume source. In contrast, nearaxis lavas show no primitive noble gas isotope signatures, but are enriched in strontium and lead, indicative of subducted former oceanic lower crust melting within the plume source5–7. We propose that, in a near-ridge setting, primitive, plumesourced magmas formed deep in the plume are preferentially channelled to and erupted at the ridge-axis. The remaining residue continues to rise and melt, forming the near-axis seamounts. With the deep melts removed, the geochemical signature of subduction contained within the residue becomes apparent. Lavas with strontium and lead enrichments are found worldwide where plumes meet mid-ocean ridges6–8, suggesting that subducted lower crust is an important but previously unrecognised plume component

Nickel and helium evidence for melt above the core–mantle boundary

High ^(3)He/^(4)He ratios in some basalts have generally been interpreted as originating in an incompletely degassed lower-mantle source. This helium source may have been isolated at the core–mantle boundary region since Earth’s accretion. Alternatively, it may have taken part in whole-mantle convection and crust production over the age of the Earth; if so, it is now either a primitive refugium at the core–mantle boundary or is distributed throughout the lower mantle. Here we constrain the problem using lavas from Baffin Island, West Greenland, the Ontong Java Plateau, Isla Gorgona and Fernandina (Galapagos). Olivine phenocryst compositions show that these lavas originated from a peridotite source that was about 20 per cent higher in nickel content than in the modern mid-ocean-ridge basalt source. Where data are available, these lavas also have high ^(3)He/^(4)He. We propose that a less-degassed nickel-rich source formed by core–mantle interaction during the crystallization of a melt-rich layer or basal magma ocean, and that this source continues to be sampled by mantle plumes. The spatial distribution of this source may be constrained by nickel partitioning experiments at the pressures of the core–mantle boundary

Optical study of strained double Ge/Si quantum dot layers

status: publishe

Photoluminescence and Raman study of a tensilely strained Si type-II quantum well on a relaxed SiGe graded buffer

status: publishe

Experimental Evidence and Modified Growth Model of Alloying in InxGa1-xAs Nanowires

status: publishe