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In the distribution transformers design oval windings are used due to economic advantages. On the other hand, such windings are more susceptible to radial forces in a short circuit. A diamond dotted paper with an epoxy coating is used in order to increase the stiffness of the winding. Despite that, winding failure may occur during the short circuit, e.g. buckling of inner winding. Because of a very thin foil conductor (typically 0.5-2 mm), the most critical is inner low voltage foil winding which can collapse due to radial forces at stresses far below the elastic limit of conductor material. This paper shows an analytical approach to the calculation of critical stress in inner oval foil winding with epoxy coated insulation. Critical stress was calculated using the equation for free buckling of round winding. Equivalent Young's modulus of elasticity was obtained experimentally from the testing of the sample model loaded with bending force on a tensile test machine. A total of 12 test samples were formed from aluminium foil conductor and diamond dotted paper and cured at the temperature of 105°C. The results were successfully verified on distribution transformers subjected to short circuit withstand tests.

Six diamond-bearing eclogite xenoliths with oceanic crust protoliths and 370 mineral inclusions in 104 diamonds recovered from the Koidu kimberlite complex in Sierra Leone provide insight into the lithological and compositional diversity of the lithospheric mantle beneath the West African Craton. Diamond formation beneath Koidu is predominantly associated with eclogitic substrates that originated from subduction and high-pressure metamorphism of oceanic crust, as indicated by a dominance of eclogitic (78%) over peridotitic (17%) and mixed paragenesis diamonds (5%). Peridotitic diamonds contain olivine inclusions with very high Mg# (92.2–94.7; median = 94.2), indicative of derivation from dunite or harzburgite protoliths. Moreover, a peridotitic spinel with Cr# = 50.9 suggests that it equilibrated with orthopyroxene-free dunite. 44% of Koidu diamonds contain coesite, of which some coexist with omphacite, eclogitic garnet, and/or kyanite. Most analysed eclogitic garnet inclusions have extremely high δ 18 O values ( ≥ + 9.9‰) and occur with clinopyroxene inclusions that have very high jadeite components (~ 70 mol%). These high jadeite components are a close match to clinopyroxenes in high-pressure metapelites, which have a phase assemblage that includes coesite and kyanite. Our data suggest that the eclogitic mineral inclusions in most Koidu diamonds have oceanic basalt protoliths that were mingled with pelagic sediments, which may have increased δ 18 O values to levels much higher than observed for other eclogites at Koidu and shifted the originally basaltic bulk compositions closer to that of pelites. Most eclogitic mineral inclusions in Koidu diamonds have elemental compositions not observed for Koidu eclogite xenoliths, which have clear oceanic crust protolith (oceanic lavas and cumulates) signatures without significant crustal sediment contamination. These findings suggest the subduction of distinct packages of oceanic crust into the Koidu lithospheric mantle through time.

Zimmi diamonds (Sierra Leone) have 500 million year mantle residency times whose origin is best explained by rapid tectonic exhumation to shallower depths in the mantle, associated with continental collision but prior to kimberlite eruption. Here we present spectroscopic data for a new suite of Zimmi sulphide-bearing diamonds that allow us to evaluate the link between their spectroscopic features and their unusual geological history. Cathodoluminesence (CL) imaging of these diamonds revealed irregular patterns with abundant deformation lamellae, associated with the diamonds’ tectonic exhumation. Vacancies formed during deformation were subsequently naturally annealed to form vacancy clusters, NV0/− centres and H3 (NVN0). The brownish-yellow to greenish-yellow colours observed in Zimmi Ib-IaA diamonds result from visible absorption by a combination of isolated substitutional nitrogen (NS0\\[ {\\mathrm{N}}_{\\mathrm{S}}^0 \\]) and deformation-related vacancy clusters. Colour-forming centres and other spectroscopic features can all be attributed to the unique geological history of Zimmi Ib-IaA diamonds and their rapid exhumation after formation.

Various types of broken rock masses, such as those in fault-fracture zones and fracture zones, which form as a result of disturbance from tunnelling, are often encountered during underground engineering construction. These rock masses have low self-supporting capacity and poor stability, which can easily cause damage to surrounding rock, such as large deformation features, collapse and falling blocks, etc., posing a threat to construction safety. During a field project, reinforcement by grouting is a primary means for addressing the aforementioned problems. The effective measurement of rock mass characteristics (e.g., rock layer interfaces and the broken area of surrounding rock) provides a basis for the reasonable design of a grouting scheme. The quantitative evaluation of the effect of rock mass grouting is essential for optimizing the grouting scheme. In view of this, in this study, a multi-functional rock mass digital drilling test system and a special polycrystalline diamond compact drill bit for digital testing were developed and were applied to conduct digital drilling tests on intact, broken and grouted rock masses. In addition, a digital drilling test (DDT) technique-based method for measuring rock mass characteristics in real time and rapidly evaluating the grouting effect was proposed. The proposed method is capable of identifying rock layer interfaces, determining the broken area and obtaining the equivalent strength of grouted rock masses. This method is advantageous for obtaining quantitative and rapid test results, which can provide a theoretical basis and technical means for optimizing the grouting parameters and designing support schemes for underground engineering construction.

The Sm–Nd isotope systematics and geochemistry of eclogitic, websteritic and peridotitic garnet and clinopyroxene inclusions together with characteristics of their corresponding diamond hosts are presented for the Letlhakane mine, Botswana. These data are supplemented with new inclusion data from the nearby (20–30 km) Orapa and Damtshaa mines to evaluate the nature and scale of diamond-forming processes beneath the NW part of the Kalahari Craton and to provide insight into the evolution of the deep carbon cycle. The Sm–Nd isotope compositions of the diamond inclusions indicate five well-defined, discrete eclogitic and websteritic diamond-forming events in the Orapa kimberlite cluster at 220 ± 80 Ma, 746 ± 100 Ma, 1110 ± 64 Ma, 1698 ± 280 Ma and 2341 ± 21 Ma. In addition, two poorly constrained events suggest ancient eclogitic (> 2700 Ma) and recent eclogitic and websteritic diamond formation (< 140 Ma). Together with sub-calcic garnets from two harzburgitic diamonds that have Archaean Nd mantle model ages (TCHUR) between 2.86 and 3.38 Ga, the diamonds studied here span almost the entire temporal evolution of the SCLM of the Kalahari Craton. The new data demonstrate, for the first time, that diamond formation occurs simultaneously and episodically in different parageneses, reflecting metasomatism of the compositionally heterogeneous SCLM beneath the area (~ 200 km2). Diamond formation can be directly related to major tectono-magmatic events that impacted the Kalahari Craton such as crustal accretion, continental breakup and large igneous provinces. Compositions of dated inclusions, in combination with marked variations in the carbon and nitrogen isotope compositions of the host diamonds, record mixing arrays between a minimum of three components (A: peridotitic mantle; B: eclogites dominated by mafic material; C: eclogites that include recycled sedimentary material). Diamond formation appears dominated by local fluid–rock interactions involving different protoliths in the SCLM. Redistribution of carbon during fluid–rock interactions generally masks any potential temporal changes of the deep carbon cycle.

A suite of coated diamonds from the International’naya (n = 63) and Mir (n = 5) kimberlite pipes (Mirny field, Siberian craton) was studied to track the most recent metasomatic events in the sub-continental lithospheric mantle (SCLM). The diamonds consist of two contrasting domains: an older monocrystalline core, and a younger fibrous coat, the latter of which formed just prior to the kimberlite eruption. Microinclusions in the coats indicate two types of growth media: (i) dominant, silicic to low-Mg carbonatitic high-density fluids (HDFs), and (ii) minor, high-Mg carbonatitic HDFs. Eclogitic mineral inclusions were identified in the cores of the diamonds containing silicic to low-Mg carbonatitic HDFs in the coats, while peridotitic mineral inclusions were found in the cores of the diamonds with high-Mg carbonatitic HDFs in the coats. The chemistry of the high-Mg carbonatitic HDFs suggests that they originated from partial melting of a carbonated peridotite. Major components and trace-element patterns of most silicic to low-Mg carbonatitic HDFs support an eclogitic source with accessory rutile and variable ratios of CO2/H2O. In many coats, the HDFs evolve from silicic to more carbonatitic, and rarely from carbonatitic to more silicic. The scenario of both evolutionary trends could have involved the passage of peridotite-derived carbonatitic HDFs into eclogites, which triggered their partial melting, followed by the appearance of immiscible, highly silicic and Ca-rich carbonatitic fluids/melts. The immiscible fluids evolved toward a single-silicate–carbonate melt, whose cooling resulted in the precipitation of silicate minerals.

Drilling into deep formation characterized by high formation and hydrostatic pressures often brings great challenges to oil and gas industry and the phenomena, such as bit slip, balling and cutter wear, are easy to be exposed. Therefore, it is very important to conduct rock-breaking experiments under high confining and hydrostatic pressures and understand the cutter–rock interaction behaviour for revealing the rock-breaking mechanism of Polycrystalline Diamond Compact (PDC) cutter. In this paper, granite, sandstone and shale were used to carry out PDC cutter cutting experiments under confining and hydrostatic pressures. Cutting force, mechanical specific energy (MSE), cuttings, cutting grooves and energy change were comprehensively analyzed when rock suffers different failure modes under different cutting conditions. The results show that hydrostatic pressure significantly increases the cutting force and MSE compared with cutting results under atmospheric pressure. In addition, different lithology of rocks leads to the different changing trends of cutting force with hydrostatic pressure and affects the pore pressure and differential pressure under hydrostatic pressures. Besides, the smoother cutting grooves and fragmentary cuttings are obtained with increased hydrostatic pressure during cutting and the mud phenomenon of cuttings is witnessed. Furthermore, the fluctuation of cutting force curve and the number of peaks and valleys in cutting force curve reveal the failure behaviour and energy change of rock during cutting. In general, the distance between peaks or valleys is small and more peaks and valleys are obtained when rock suffers ductile failure. Meanwhile, the energy absorption time of rock is shorter and the small-sized cuttings are obtained. Conversely, the distance between peaks or valleys is large and less peaks and valleys are produced when rock suffers brittle failure and the energy absorption time of rock is longer and large-sized cuttings are obtained. Although hydrostatic pressure tends to change the failure mode of rock from brittle to ductile, the number of peaks and valleys in the cutting force curves obtained under hydrostatic pressures is less. The experimental results provide a new understanding of the failure behaviour of rocks and cutter–rock interaction under different cutting conditions.HighlightsRocks cutting experiments with three kinds of rocks under confining and hydrostatic pressures were conducted to truly simulate the rock-breaking process of bit at the bottom of the well.The rock-breaking performance of PDC single cutter under hydrostatic pressures was analyzed from the aspects of mechanical specific energy, cuttings, cuttings morphology and cutting groove.The rock failure behaviour and the cutter–rock interaction under hydrostatic pressures were studied from the perspectives of fluctuation of cutting force curve, cuttings formation process and energy change during cutting process.The influence of lithology on failure process and pore pressure of rock was initially investigated through rock soaking experiments.

The quantum spin properties of nitrogen-vacancy defects in diamond enable diverse applications in quantum computing and communications 1 . However, fluorescent nanodiamonds also have attractive properties for in vitro biosensing, including brightness 2 , low cost 3 and selective manipulation of their emission 4 . Nanoparticle-based biosensors are essential for the early detection of disease, but they often lack the required sensitivity. Here we investigate fluorescent nanodiamonds as an ultrasensitive label for in vitro diagnostics, using a microwave field to modulate emission intensity 5 and frequency-domain analysis 6 to separate the signal from background autofluorescence 7 , which typically limits sensitivity. Focusing on the widely used, low-cost lateral flow format as an exemplar, we achieve a detection limit of 8.2 × 10 −19 molar for a biotin–avidin model, 10 5  times more sensitive than that obtained using gold nanoparticles. Single-copy detection of HIV-1 RNA can be achieved with the addition of a 10-minute isothermal amplification step, and is further demonstrated using a clinical plasma sample with an extraction step. This ultrasensitive quantum diagnostics platform is applicable to numerous diagnostic test formats and diseases, and has the potential to transform early diagnosis of disease for the benefit of patients and populations. Lateral-flow in vitro diagnostic assays based on fluorescent nanodiamonds, in which microwave-based spin manipulation is used to increase sensitivity, are demonstrated using the biotin–avidin model and by the single-copy detection of HIV-1 RNA.

The existence of confining pressure is an important factor that can’t be ignored in rock cutting process. Rocks show high strength and strong plasticity under confining pressure condition (CPC), leading to the low rock-breaking efficiency of drilling bit, which is more prominent in deep formation drilling. However, the understanding of rock-breaking mechanism of Polycrystalline Diamond Compact (PDC) cutter under CPC is still unclear. Given that fact, in this paper, a series of rock cutting experiments on sandstone and granite under different confining pressures and atmospheric pressure conditions were carried out using a self-made true triaxial rock cutting device. The cutting force, mechanical specific energy (MSE) and cuttings mass fraction under confining pressure and atmospheric pressure conditions were studied, and the cutting grooves were analyzed. The results show that the existence of confining pressure greatly increases the difficulty of rock cutting, which is embodied by the increase of cutting force and MSE. In addition, the size of cuttings produced under CPC is smaller, and the proportion of powdery cuttings increases with increasing confining pressure. Meanwhile, the cutting grooves obtained under CPCs are smoother. Microscopically, the existence of confining pressure greatly enhances the contact stress between PDC cutter and rock, resulting in a larger area of dense core when PDC cutter contacts with rock. Confining pressure leads to the difficulty of cuttings discharge to a certain extent, which easily results in the secondary and repeated destruction of cuttings and increases the energy dissipation. In general, confining pressure leads to the lower damage degree of PDC cutter to the rock, which makes the rock difficult to be drilled. The research results can provide some special guidance for rock breaking in deep formation, and provide practical thoughts and enlightenment for rock breaking, bits arrangement and optimization under CPC.HighlightsThe cutting experiments under confining pressure condition are carried out by using the self-made rock cutting device that exerts three-dimensional stress on rock, which truly simulates the rock breaking process at the bottom of the well.The rock-breaking performances under atmospheric pressure condition and confining pressure conditions are comprehensively analyzed from the aspects of cuttings mass fraction, cuttings size, cutting groove and coarseness index.The rock-breaking mechanism of PDC cutter under confining pressure condition is investigated and the rock-breaking behavior of PDC cutter under confining pressure condition is studied.Three kinds of changing trends of mechanical specific energy with confining pressure are put forward, and the concept of confining pressure threshold is also proposed.

This article reviews the state of the art in inversion-type p-channel diamond MOSFETs. We successfully developed the world’s first inversion-channel homoepitaxial and heteroepitaxial diamond MOSFETs. We investigated the dependence of phosphorus concentration ( N P ) of the n-type body on field-effect mobility ( μ FE ) and interface state density ( D it ) for the inversion channel homoepitaxial diamond MOSFETs. With regard to the electrical properties of both the homoepitaxial and heteroepitaxial diamond MOSFETs, they suffer from low μ FE and one main reason is high D it . To improve the interface quality, we proposed a novel technique to form OH-termination by using H-diamond followed by wet annealing, instead of the previous OH-termination formed on O-diamond. We made precise interface characterization for diamond MOS capacitors by using the high-low C–V method and the conductance method, providing further insights into the trap properties at Al 2 O 3 /diamond interface, which would be beneficial for performance enhancement of the inversion-type p-channel diamond MOSFETs. Graphic abstract