The microwave-assisted rock fragmentation has been proven to be a promising approach in reducing cutting tools wear and improving efficiency in rock crushing and excavation. Thus, understanding the ...influence of damage induced by microwave irradiation on rock fragmentation is necessary. In this context, cylindrical Fangshan granite (FG) specimens were exposed to microwave irradiation at a power of 6 kW for different durations up to 4.5 min. The damages of the specimens induced by irradiation were quantified by using both X-ray micro-CT scanning and ultrasonic wave measurement. The CT value and P-wave velocity decreased with increase of irradiation duration. The irradiated specimens were then tested using a split Hopkinson pressure bar (SHPB) system to simulate rock fragmentation. A momentum-trap technique was utilized to ensure single-pulse loading on the specimen in SHPB tests, enabling valid fragment size distribution (FSD) analysis. The dependence of dynamic uniaxial compressive strength (UCS) on the irradiation duration and loading rate was revealed. The dynamic UCS increased with increase of loading rate while decreased with increase of irradiation duration. Using the sieve analysis, three fragmentation types were proposed based on FSD, which were dictated by both loading rate and irradiation duration. In addition, an average fragment size was proposed to quantify FSD. The results showed that the average fragment size decreased with increase of loading rate. A loading rate range was identified, where a dramatic reduction of the average fragment size occurred. The dependence of fragmentation on the irradiation duration and loading rate was also discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
High stress induced by excavation disturbance in deep hard rock engineering can cause rockburst accidents. Microwave-induced borehole fracturing of hard rock is a promising technique for preventing ...rockbursts, the principle of which is to reduce energy and stress concentration levels in rock mass through microwave heating. The characteristics and mechanism of microwave-induced borehole fracturing of hard rock under different true triaxial stresses were experimentally investigated. After microwave-induced borehole fracturing under different σ1 and σ2 conditions, a complex crack network dominated by tensile cracks was generated in the rock specimen, which is consistent with the results obtained by AF and RA. According to the P-wave velocity before and after the test, the degree of thermal fracture is positively linearly correlated with σ1 and σ2 as a whole, and has good consistency with the length and number of thermal cracks. The results show that the technique will have better applicability and higher fracturing efficiency in high-stress areas. The thermal fracture process of basalt specimens under different σ1 and σ2 conditions is similar, which can be divided into a silent period, quiet period, dense period, and persistent period. In addition, thermal fracture exerts a significant threshold temperature effect, and fracture rate increases rapidly when the temperature reaches 150–192 °C (average about 172 °C). The relationship between thermal fracture and stress provides guidance for parameter design.
•Microwave-induced borehole fracturing of hard rock is a promising technique for preventing rockbursts.•Microwave-induced borehole fracturing tests are conducted under different true triaxial stress.•The characteristics and mechanism of microwave-induced borehole fracturing under different σ1 and σ2 conditions are investigated.•Microwave-induced borehole fracturing process is investigated by AE technique.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZRSKP
In order to understand the influence of different factors on the microwave response characteristics of ores, the effects of electrical conductivity, metal mineral content, compactness, metal mineral ...distribution, microwave frequency and temperature on the dielectric properties of synthetic ores (metal mineral and quartz) were studied. Microwave heating tests were carried out on three types of natural ores (Hongtoushan copper ore, Sishanling iron ore and Dandong gold ore) with significant differences in metal mineral contents. The test results showed that under microwave irradiation, the stronger the electrical conductivity of the metal minerals, the smaller the penetration depth in synthetic ore. For those metal minerals with lower electrical conductivity, the microwave absorption coefficient of the synthetic samples increases with increasing metal mineral content. For those metal minerals with higher electrical conductivity, the microwave absorption coefficient of the samples first increases and then decreases as the metal mineral content increases. When the metal minerals are distributed in layers, the penetration depth is much less than that given a uniform distribution. The penetration depth in the sample at microwave frequency of 915 MHz is greater than that at 2.45 GHz. The higher the electrical conductivity of metal minerals used in synthetic ores, the higher the high-temperature sensitivity of electromagnetic shielding coefficient (0 °C–500 °C). The Hongtoushan copper ore with high metal mineral content exhibits obvious size effect. The effects of ore structure and crystal particle size on the distribution characteristics of microcracks were discussed. Based on the test results, a quantitative prediction model of microwave sensitivity of ore was proposed, which provides guidance for the prediction of ore heating effect and the selection of microwave heating sequence of ore.
•The microwave response characteristics of ore was studied by means of dielectric properties of synthetic samples.•The effects of conductivity and content of metallic minerals on microwave response characteristics of ores were studied.•A predictive model of microwave sensitivity and microwave heating order of ore is proposed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Microwave-assisted mechanical excavation has great application prospects in mines and tunnels, but there are few field experiments on microwave-assisted rock breaking. This paper takes the Sishanling ...iron mine as the research object and adopts the self-developed high-power microwave-induced fracturing test system for hard rock to conduct field experiments of microwave-induced fracturing of iron ore. The heating and reflection evolution characteristics of ore under different microwave parameters (antenna type, power, and working distance) were studied, and the optimal microwave parameters were obtained. Subsequently, the ore was irradiated with the optimal microwave parameters, and the cracking effect of the ore under the action of the high-power open microwave was analyzed. The results show that the reflection coefficient (standing wave ratio) can be rapidly (<5 s) and automatically adjusted below the preset threshold value (1.6) as microwave irradiation is performed. When using a right-angle horn antenna with a working distance of 5 cm, the effect of automatic reflection adjustment reaches the best among other antenna types and working distances. When the working distance is the same, the average temperature of the irradiation surface and the area of the high-temperature area under the action of the two antennas (right-angled and equal-angled horn antenna) are basically the same and decrease with the increase of working distance. The optimal microwave parameters are: a right-angle horn antenna with a working distance of 5 cm. Subsequently, in further experiments, the optimal parameters were used to irradiate for 20 s and 40 s at a microwave power of 60 kW, respectively. The surface damage extended 38 cm × 30 cm and 53 cm × 30 cm, respectively, and the damage extended to a depth of about 50 cm. The drilling speed was increased by 56.2% and 66.5%, respectively, compared to the case when microwaves were not used.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Microwave pre-treatment is considered as a promising technique for alleviating cutter wear. This paper introduces a high-power microwave-induced fracturing system for hard rock. The test system ...consists of a high-power microwave subsystem (100 kW), a true triaxial testing machine, a dynamic monitoring subsystem, and an electromagnetic shielding subsystem. It can realize rapid microwave-induced fracturing, intelligent tuning of impedance, dynamic feedback under strong microwave fields, and active control of microwave parameters by addressing the following issues: the instability and insecurity of the system, the discharge breakdown between coaxial lines during high-power microwave output, and a lack of feedback of rock-microwave response. In this study, microwave-induced surface and borehole fracturing tests under true triaxial stress were carried out. Experimental comparisons imply that high-power microwave irradiation can reduce the fracturing time of hard rock and that the fracture range (160 mm) of a 915-MHz microwave source is about three times that of 2.45 GHz. After microwave-induced borehole fracturing, many tensile cracks occur on the rock surface and in the borehole: the maximum reduction of the P-wave velocity is 12.8%. The test results show that a high-power microwave source of 915 MHz is more conducive to assisting mechanical rock breaking and destressing. The system can promote the development of microwave-assisted rock breaking equipment.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Iron-sulfur proteins play essential roles in a wide variety of cellular processes such as respiration, photosynthesis, nitrogen fixation and magnetoreception. The stability of iron-sulfur clusters ...varies significantly between anaerobic and aerobic conditions due to their intrinsic sensitivity to oxygen. Iron-sulfur proteins are well suited to various practical applications as molecular redox sensors or molecular “wires” for electron transfer. Various technologies have been developed recently using one particular iron-sulfur protein, MagR, as a magnetic tag. However, the limited protein stability and low magnetic sensitivity of MagR hindered its wide application. Here in this study, the iron-sulfur binding site of pigeon clMagR was rationally re-designed. One such mutation, T57C in pigeon MagR, showed improved iron-sulfur binding efficiency and higher iron content, as well as prolonged thermostability. Thus, clMagR
T57C
can serve as a prototype for further design of more stable and sensitive magnetic toolbox for magnetogenetics in the future.
This article introduces a high-power microwave mechanical integrated continuous mining device, which can achieve synchronous cutting of hard rocks by microwave and machinery. The device includes a ...cutting system, a rotary translation system, a loading system, a high-power microwave system, and a control and monitoring system. The technology of “master-slave follow-up” disc cutter alternating side cutting of rock was proposed, which could improve the effectiveness of rock breaking. The integrated structure of a microwave-cut system was then proposed, and synchronous motion of the microwave-cut system and adjustment of the loading system could be realized. The automatic adjustment technology of the microwave working distance was developed to dynamically control the optimal microwave working distance. The basic functions of the equipment were verified by tests. By comparing the two types of disk cutters, it is found that the master-slave follow-up disk cutter can improve significantly the dust removal effect and rock breaking efficiency in rock breaking process versus the conventional large disc cutter. Cutting tests of slate with or without microwave were conducted using a master-slave follow-up disk cutter. The results show that the cutting patterns of slates change from intermittent chunks (without microwave irradiation) to persistent debris (with microwave irradiation), and the cutting speed is significantly improved (170%). The development of the device provides a scientific basis for changing the conventional mining technology of metal mines and realizing the mechanical continuous mining in hard metal mines.
•A microwave mechanical integrated continuous mining device was invented.•The reliability and innovation of the equipment were proven through calibration tests.•Compared with that under no microwave condition, the rock-breaking efficiency is improved under microwave irradiation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Microwave-assisted mechanical mining is a new mining method with great potential. A self-developed true triaxial system for microwave-induced fracturing and cutting of hard rocks was used to study ...the microwave cracking process, cracking mechanism, and its effects on subsequent cutting, grinding and mineral dissociation by taking Sishanling banded iron ore as the research object. The results show that compared with microwave irradiation alone, the failure mode and mechanism of ore samples were more complex under the combined action of true triaxial stress and microwaves. Large cracks that were parallel to the bedding plane appeared in the sample under microwave irradiation without triaxial stress. When true triaxial stress and microwave irradiation were used simultaneously, the surface of the sample was subject to spalling or spalling and cracking. Additionally, the correlation (parallel or vertical) between the direction of σ1 and the direction of the bedding plane affected the fracture characteristics. Microwave irradiation could promote subsequent mechanical mining, grinding, and beneficiation of samples. Compared with no microwave treatment, under the action of stress and microwaves, the total amount of rock breakage of samples was increased by 55.1%, the powder content of the product after grinding of cut particles was increased by 21.9%, and the degrees of dissociation of cutting products (<0.1 mm and <0.2 mm) were increased by 11.6 and 12.7%, respectively. The influence of the strip width of magnetite on the microwave cracking effect of ore was estimated. At a given magnetite content, the microwave absorption was worse for wider strips, and the reflection performance was similar for strips of various widths.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Iron-sulfur clusters are essential cofactors for proteins involved in various biological processes, such as electron transport, biosynthetic reactions, DNA repair, and gene expression regulation. ...Iron-sulfur cluster assembly protein IscA1 (or MagR) is found within the mitochondria of most eukaryotes. Magnetoreceptor (MagR) is a highly conserved A-type iron and iron-sulfur cluster-binding protein, characterized by two distinct types of iron-sulfur clusters, 2Fe-2S and 3Fe-4S, each conferring unique magnetic properties. MagR forms a rod-like polymer structure in complex with photoreceptive cryptochrome (Cry) and serves as a putative magnetoreceptor for retrieving geomagnetic information in animal navigation. Although the N-terminal sequences of MagR vary among species, their specific function remains unknown. In the present study, we found that the N-terminal sequences of pigeon MagR, previously thought to serve as a mitochondrial targeting signal (MTS), were not cleaved following mitochondrial entry but instead modulated the efficiency with which iron-sulfur clusters and irons are bound. Moreover, the N-terminal region of MagR was required for the formation of a stable MagR/Cry complex. Thus, the N-terminal sequences in pigeon MagR fulfil more important functional roles than just mitochondrial targeting. These results further extend our understanding of the function of MagR and provide new insights into the origin of magnetoreception from an evolutionary perspective.
The morphology is the consequence of evolution and adaptation. Escherichia coli is rod-shaped bacillus with regular dimension of about 1.5 μm long and 0.5 μm wide. Many shape-related genes have been ...identified and used in morphology engineering of this bacteria. However, little is known about if specific metabolism and metal irons could modulate bacteria morphology. Here in this study, we discovered filamentous shape change of E. coli cells overexpressing pigeon MagR, a putative magnetoreceptor and extremely conserved iron-sulfur protein. Comparative transcriptomic analysis strongly suggested that the iron metabolism change and iron accumulation due to the overproduction of MagR was the key to the morphological change. This model was further validated, and filamentous morphological change was also achieved by supplement E. coli cells with iron in culture medium or by increase the iron uptake genes such as entB and fepA. Our study extended our understanding of morphology regulation of bacteria, and may also serves as a prototype of morphology engineering by modulating the iron metabolism.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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