Hard Conditions Research Articles

Reliability Analysis of Mining Machinery Pick Subject to Competing Failure Processes With Continuous Shock and Changing Rate Degradation

Efficient mining machinery operation is essential for coal mining enterprises to reduce production costs, improve production efficiency, and maximize profits. As a key consumable part of mining machinery, the reliability of the pick directly determines the operational performance and service life of the machinery. During the mining process, the pick can be affected by natural wear and tear caused by the coal and rock and load shocks caused by the gangue and faults—that is, the result of the competing influence of soft failure caused by natural wear and tear and hard failure caused by random load shocks. At the same time, because the gangue and faults have a certain volume and hardness, a random load shock may last for a certain period of time, producing different acceleration effects on the pick wear under different hardness conditions. In this article, the reliability modeling of the pick competing failure process under random load shocks was studied by considering the influence of continuous shocks and the accelerated degradation at changing rates for different shock durations on the pick wear. First, the pick degradation model under random load shocks was established by considering the natural wear degradation, instantaneous shock degradation, and accelerated degradation at changing rates for different shock durations. Second, the pick reliability model under the competing failure mode was established on this basis. Finally, a numerical experiment and an effectiveness analysis of the pick reliability model were conducted based on the engineering data. The results showed that the competing failure reliability model of the pick considering continuous shocks and a changing degradation rate was more in line with engineering practice, which is of great significance for pick design optimization and improved reliability.

The Digital Aesthetic Test Drive.

The burgeoning public interest in techniques to enhance a smile has led to demand on clinicians that require important steps in the pre-treatment approval process. Digital dentistry provides a new level of planning and visualisation, improving clinical risk assessment and patient engagement. Dentists must acquire a sound understanding of aesthetic design parameters, including physiologic limitations, and must match patient expectations with clinical reality. Digital design offers flexibility not obtainable with the conventional analogue wax up. Multiple versions of a design can be viewed in a 2D or 3D simulation and accommodated efficiently in CAD software, with 3D printed models generated from each design. The ability to use a test drive or mock-up based on a 3D digital analysis and design, has created a new standard of care for treatment planning, providing an accurate and reversible preview before any definitive dentistry is done. It also places the responsibility for understanding biologic limitations of care on the general dentist, with the risk that digital planning may over-promise if not matched with underlying hard and soft tissue conditions. It improves interdisciplinary and laboratory communication and increases the predictability of the proposed treatment. The result is greater patient satisfaction and an improved informed consent process.

Simulation model for pulse width modulation-voltage source inverter of three-phase induction motor

Induction motor has been widely applied in many sectors, as it has the advantages of simplicity, toughness and can withstand hard environment conditions. The working of such motor in constant voltage/frequency (V/F) speed control method has been popular since the introduction of the power electronic devices, which consequently make the implementation of this method simpler and effectives. The V/F speed control is dominated choice for many applications, especially open loop control and also for closed loop control when the accuracy is not a crucial issue. This study deals with two cases of controlling open and close of the electronic switches. The first with equal intervals by placing regular pulses at the opening and closing periods, and the second using three-phase pulse width generator, through which the control of different periods is carried out according to the required control. Four models have been simulated in this study including, three-phase induction motor at constant torque (constant load) as well as at variable torque (variable load), modeling of PWM-VSI for three-phase induction motor at constant torque (constant load) as well as at variable torque (variable load). The results have shown that speed profile of the IM can be improved by controlling the invertor using PWM technique.

Integral Quadratic Constraints with Infinite-Dimensional Channels.

Modern control theory provides us with a spectrum of methods for studying the interconnection of dynamic systems using input-output properties of the interconnected subsystems. Perhaps the most advanced framework for such input-output analysis is the use of Integral Quadratic Constraints (IQCs), which considers the interconnection of a nominal linear system with an unmodelled nonlinear or uncertain subsystem with known input-output properties. Although these methods are widely used for Ordinary Differential Equations (ODEs), there have been fewer attempts to extend IQCs to infinite-dimensional systems. In this paper, we present an IQC-based framework for Partial Differential Equations (PDEs) and Delay Differential Equations (DDEs). First, we introduce infinite-dimensional signal spaces, operators, and feedback interconnections. Next, in the main result, we propose a formulation of hard IQC-based input-output stability conditions, allowing for infinite-dimensional multipliers. We then show how to test hard IQC conditions with infinite-dimensional multipliers on a nominal linear PDE or DDE system via the Partial Integral Equation (PIE) state-space representation using a sufficient version of the Kalman-Yakubovich-Popov lemma (KYP). The results are then illustrated using four example problems with uncertainty and nonlinearity.

Structural behavior of a seismic-isolated stadium grandstand considering hard and soft soil conditions

La principal aplicación del aislamiento sísmico a nivel mundial está en edificaciones y puentes, sin embargo, puede ser aplicada a cualquier estructura. La técnica, teóricamente, tiene limitaciones de uso por eficiencia, como en edificaciones altas y suelos blandos. En este artículo se estudia una estructura aislada no convencional, para evaluar los beneficios del aislamiento sobre esta. Específicamente se analiza una tribuna de estadio localizada en Colombia, con condiciones de suelo duro y blando. La estructura es importante, debido a su necesidad de mitigación del riesgo por sismo. Esta considerará un alto número de personas que deben evacuar de forma segura durante terremotos y después de estos, la estructura podría ser destinada a refugio humanitario. Los resultados a) muestran beneficio estructural principalmente en condiciones de suelo duro, b) corroboran y cuantifican las limitaciones de los suelos blandos y c) permiten generar algunas recomendaciones para aislar estructuras bajo las condiciones aquí estudiadas.

Paralleled multi-GaN MIS–HEMTs integrated cascode switch for power electronic applications

A cascode gallium nitride (GaN) switch integrating four paralleled GaN depletion-mode metal–insulator–semiconductor–high-electron-mobility transistors (MIS–HEMT) and a silicon MOSFET (Si-MOSFET) is presented. Each GaN chip is wire-bonded into a multi-chip power module to scale up the power rating. An optimized symmetric configuration and wire bonding of an integral package are used in the cascode switch. By utilizing an optimized packaging approach, the performance of the multi-GaN-chip cascode switch was evaluated through both static and dynamic characterizations. The constructed cascode switch provides a low-static on-state resistance of 72 mΩ and an off-state blocking capability of 400 V with a positive threshold voltage of 2 V. Analysis of dynamic switching characteristics are discussed and demonstrates stable dynamic on-state resistance (R DS-ON) in inductive load circuits with switching dependencies of voltage, frequency, time, and temperature. The extended defects from buffer caused a minimal decrease in dynamic and static R DS-ON with respect to hard switching conditions. However, there was no noticeable degradation in R DS-ON under harsh switching conditions. This study provides a complete analysis of the multi-GaN-chip cascode switch, including MIS–HEMT manufacturing, cascode packaging and static and dynamic characterizations.

Elemental determination in carbon nanotubes by inductively coupled plasma optical emission spectrometry after a greener and simple microwave-assisted digestion method

A method for the determination of elemental contaminants and metal catalyst residues (Al, Ca, Co, Cr, Fe, La, Mg, Mo, Ni, and Zn) in carbon nanotubes (CNTs) by inductively coupled plasma optical emission spectrometry (ICP OES) was developed by optimizing a greener digestion protocol for sample preparation. The feasibility of using a diluted nitric acid solution combined with H2O2 and high air flow-rate outside the digestion vessel during the microwave-assisted heating was evaluated. Complete digestion of up to 100 mg of CNT was possible using 6 mL of 1 mol L−1 HNO3 combined with 2 mL of 30% w w−1 H2O2, and 125 m3 h−1 of air flow-rate outside the digestion vessel during microwave heating. Comparison of the results obtained using the proposed method with those using a comparative method described in the literature was carried out. Accuracy was also evaluated by comparison of results with those by neutron activation analysis (NAA), and no statistical difference was observed. Limits of quantification (LOQ) ranged from 0.86 (Co) to 4.12 μg g−1 (Ca). Digests obtained using the proposed method were adequate for reliable determinations by ICP OES, and can be alternatively used for routine quality control of metal catalyst residues or impurities in CNTs. Moreover, the proposed method agrees with the recommendations of green analytical chemistry, bringing an important contribution to the sample preparation of CNTs, which normally involves hard conditions and time-consuming protocols and only allows digestion of very limited sample masses (up to 25 mg).

Operation-induced degradation mechanisms of 275-nm-band AlGaN-based deep-ultraviolet light-emitting diodes fabricated on a sapphire substrate

Degradation mechanisms of 275-nm-band AlxGa1-xN multiple quantum well deep-ultraviolet light-emitting diodes fabricated on a (0001) sapphire substrate were investigated under hard operation conditions with the current of 350 mA and the junction temperature of 105 °C. The optical output power (Po) initially decreased by about 20% within the operating time less than 102 h and then gradually decreased to about 60% by 484 h. For elucidating the causes for the initial and subsequent degradations, complementary electrical, time-resolved photoluminescence (TRPL), and impurity characterizations were carried out making a connection with the energy band profiles. Because the degradation of the wells was less significant than the Po reduction, the initial degradation is attributed essentially to the decrease in carrier injection efficiency (ηinjection), not in internal quantum efficiency of the wells, most likely due to depassivation of initially H-passivated preexisting nonradiative recombination centers (NRCs) in a Mg-doped p-type Al0.85Ga0.15N electron blocking layer. The principal cause for the subsequent Po reduction until 484 h is attributed to further decrease in ηinjection due to the appearance of certain current bypasses in addition to continuous depassivation of the NRCs in p-type AlxGa1-xN layers. According to our database on the species of vacancy-type defects acting as NRCs in GaN and AlN, which have been identified using the combination of positron annihilation and TRPL measurements, vacancy clusters comprised of a cation vacancy (VIII) and nitrogen vacancies (VN), such as VIIIVN2∼4, are the most suspicious origins of the NRCs in Mg-doped p-type AlxGa1-xN layers.

Exergaming in older adults: the effects of game characteristics on brain activity and physical activity.

Exergames are increasingly used in rehabilitation settings for older adults to train physical and cognitive abilities. To meet the potential that exergames hold, they need to be adapted to the individual abilities of the player and their training objectives. Therefore, it is important to know whether and how game characteristics affect their playing. The aim of this study is to investigate the effect of two different kinds of exergame (step game and balance game) played at two difficulty levels on brain activity and physical activity. Twenty-eight older independently living adults played two different exergames at two difficulty levels each. In addition, the same movements as during gaming (leaning sideways with feet in place and stepping sideways) were performed as reference movements. Brain activity was recorded using a 64-channel EEG system to assess brain activity, while physical activity was recorded using an accelerometer at the lower back and a heart rate sensor. Source-space analysis was applied to analyze the power spectral density in theta (4 Hz-7 Hz) and alpha-2 (10 Hz-12 Hz) frequency bands. Vector magnitude was applied to the acceleration data. Friedman ANOVA revealed significantly higher theta power for the exergaming conditions compared to the reference movement for both games. Alpha-2 power showed a more diverse pattern which might be attributed to task-specific conditions. Acceleration decreased significantly from the reference movement to the easy condition to the hard condition for both games. The results indicate that exergaming increases frontal theta activity irrespective of type of game or difficulty level, while physical activity decreases with increasing difficulty level. Heart rate was found to be an inappropriate measure in this population older adults. These findings contribute to understanding of how game characteristics affect physical and cognitive activity and consequently need to be taken into account when choosing appropriate games and game settings for exergame interventions.

캘더콧 수상작에 나타난 동물 형상화의 양상

This article aims to discuss animal-focused Caldecott winners in order to explore the way in which anthropocentric perspectives are projected onto animals, the animal wildness erupts through artificial coverings, and animals and humans meet in the wild. The act of feeding and helping animals is based on a highly human-centered setting that makes animals live and feel happy even in hard conditions, as depicted in Make Way for Ducklings, The Big Snow, and Song of the Swallows. The relationship between Genevieve and Madeline in Madeline’s Rescue shows that animals have risen to the status of friends living together, instead of being typified as inferior creatures. On the other hand, references to zoo tigers in Madeline’s Rescue lead to rethinking of the meaning of animals located in a separate space called a zoo, unlike pets, as in The Biggest Bear, May I Bring a Friend?, A Sick Day for Amos McGee, and Finding Winnie: The True Story of the World’s Most Famous Bear. Zoos are exposed to the fundamental problems implied by the observation that the zoo animals have been deprived of wildness. The wild energy of the animal as a “living creature” breaks through the cracks of the homopocentric layers no matter how hard the layers try to cover the energy, which is portrayed in The Three Pigs, Where the Wild Things Are, Jumanji, and Tuesday. A possible union of an animal and a human is hinted in The Girl Who Loved Wild Horses, but it is almost impossible to capture the scene with human language. Owl Moon and Wolf in the Snow demonstrate how hard it would be to try to reach the reality of the animal in the wild under the cover of human language. Not relying on any other human language than onomatopoeia, which translates the sounds of animals into symbols as they are heard, Owl Moon and Wolf in the Snow trace meaningful encounters between animals and humans in the wild.

Some Physiological Responses of Native Sheep Breeds to Environmental Conditions during Grazing in Natura 2000 Habitats

The calcareous xerothermic grasslands of the Festuco-Brometea class are among the most endangered Natura 2000 sites in Europe. The greatest threats include a lack of grazing, secondary succession, and invasive alien and expansive native species. The abandonment of such grasslands is caused by the low nutritional value of biomass, as well as by difficult habitat conditions. The aim of this study was to assess the physiological responses of native sheep breeds to hard environmental conditions when grazing in Natura 2000 habitats and to confirm the hypothesis that native sheep of the Świniarka and Uhruska breeds can be used to protect valuable natural habitats. The analysed grasslands were characterised by very difficult climatic and edaphic conditions and a low fodder value for sheep. Grazing in environmentally valuable areas, sometimes poor in fodder, did not adversely affect the welfare of grazed sheep. In both the Uhruska and Świniarka breeds, there were no indicators for heat or nutritional stress, but physiological changes were observed in the animals’ adaptation to new environmental conditions. Despite poor fodder positions, Świniarka sheep improved their condition and body weight. Fluctuations in indicators showing an adaptation process were also visible.

Tribological behaviour and wear mechanism of ADI with different hardness values

The tribological behaviour and wear mechanism of austempered ductile iron (ADI) with different hardness values were investigated. Results showed that the wear resistance of ADI was sensitive to hardness and service conditions. Under mild wear conditions, the low-hardness ADI sample exhibited high wear resistance because graphite was easy to transfer to the tribosurface and acted as a lubricant to reduce the friction coefficient. However, the high-hardness ADI sample was hard to deform plastically, which restricted the transfer of graphite from the matrix to the tribosurface. Under severe wear conditions, the plastic deformation of the low-hardness ADI sample gave rise to abrasive wear, which resulted in poor wear resistance. With the deterioration of wear conditions, the wear mechanism of ADI was transformed from micro-cutting wear to oxidative wear.

Moringa oleifera: A Sustainable Intervention To Address Malnutrition and Poverty in Khyber Pakhtunkhwa (KPK)- Pakistan

Rural inhabitants' lifestyles and health are greatly impacted by the recent growth in modernity,urbanization, and commercial farming as well as the loss of plant resources. Food should be consumed inthe era of incredible multi-functionality and objectivity not only to energize and feed us but also to fightagainst many illnesses and diseases and boost our immune systems. In rising nations like Pakistan, such astrategy is absolutely needed. Moringa oleifera is a very useful and versatile tree popularly named Suhanjnain Punjab, Pakistan. The Moringa tree is cultivated predominantly in semi-arid, subtropical, and tropicalenvironments. The M. oleifera belongs to the family Moringaceae is native to the sub-Himalayan areas ofPakistan, India, Bangladesh, and Afghanistan, and is grown internationally. In Pakistan, it is foundcommonly in southern Punjab and it is also considered the origin of Moringa plant. This plant has thepotential to thrive in any kind of soil and can endure extremely hard conditions. Moringa has remarkablenutritive value and it is a rich source of protein, vitamins (A & C), and micro-nutrients (Ca, K, Fe, etc.) thatare completely absent in the daily diet of the majority of the rural parts of KPK. Since 1998, the WHO haspushed Moringa as an alternative to imported food supplies to cure malnutrition in disadvantaged nations.Research has indicated that the dried leaves of Moringa contain 7 times more vitamin C than orange, 10times vitamin A than carrot, 17 times Ca than milk, 15 times K than bananas, 25 times Fe than spinach and9 times proteins than yogurt. In addition, it includes vitamin B-Complex, chrome, Cu, Mg, Mn, P and Zn.Its leaves are a great source of protein and may be exploited to combat malnutrition. In KPK, Moringaplanting and distribution have significant potential to promote farm income, improve nutrition, build upfood security, give a livelihood for rural people, stimulate rural development, and assist sustainable landcare.

Phonological and Semantic Specialization in 9- to 10-Year-Old Children During Auditory Word Processing.

One of the core features of brain maturation is functional specialization. Previous research has found that 7- to 8-year-old children start to specialize in both the temporal and frontal lobes. However, as children continue to develop their phonological and semantic skills rapidly until approximately 10 years old, it remained unclear whether any changes in specialization later in childhood would be detected. Thus, the goal of the current study was to examine phonological and semantic specialization in 9- to 10-year-old children during auditory word processing. Sixty-one children were included in the analysis. They were asked to perform a sound judgment task and a meaning judgment task, each with both hard and easy conditions to examine parametric effects. Consistent with previous results from 7- to 8-year-old children, direct task comparisons revealed language specialization in both the temporal and frontal lobes in 9- to 10-year-old children. Specifically, the left dorsal inferior frontal gyrus showed greater activation for the sound than the meaning task whereas the left middle temporal gyrus showed greater activation for the meaning than the sound task. Interestingly, in contrast to the previously reported finding that 7- to 8-year-old children primarily engage a general control region during the harder condition for both tasks, we showed that 9- to 10-year-old children recruited language-specific regions to process the more difficult task conditions. Specifically, the left superior temporal gyrus showed greater activation for the phonological parametric manipulation whereas the left ventral inferior frontal gyrus showed greater activation for the semantic parametric manipulation.

Experimental Investigation of Application Taguchi Method to Optimize Heat Treatment Parameters Using Nanofluids of AISI 52100 Steel

The present work describes a heat treatment procedure using nanofluids as quenchants for (AISI 52100 Steel) via the Taguchi method to optimize process parameters. The nanofluids have been prepared from nanoparticles (SiO2, SiC and Fe2O3) and base media consist of distilled water, toluene and ethylene glycol of volume concentrations of 0.02, 0.04 and 0.06 %. The present investigation considers hardness and wear rate as optimization criteria. The experimental variables that were selected for this study are: (austenitizing and tempering temperature), (type and volume fraction of nanoparticles) and (base media). They represent significant factors that influence on these optimization criteria. (AL18 orthogonal array), (analysis of variances (ANOVA)) and (signal/noise ratio (S/N)) were applied by means of (Minitab 18) software to examine the performance characteristics of the process parameters. The analysis of (S/N) ratio shows that the most significant parameters that give the optimum heat treatment conditions for hardness of the examined steel (AISI 52100) are: (austenitizing temperature of 800°C), (distilled water as a type of base media) and (tempering temperature of 180°C), in addition to (Fe2O3 as a nanoparticles type) and finally (nanoparticles volume fraction of 0.06%). In contrast, for the wear rate, they were: (austenitizing temperature of 800°C), type of base media (distilled water), tempering temperature of (180°C), and volume fraction of nanoparticles (0.06%) tempering. Finally, nanoparticles type (Fe2O3) is the most significant parameter for hardness and wear rate. ANOVA, exhibited that the austenitizing temperature has major effect on producing high values of hardness and wear rate for the AISI 52100 Steel.

Near Ultraviolet Photoresponse of a Silicon Carbide and Tantalum Boride Heterostructure

Silicon carbide (SiC) is widely used in abrasives, heating devices, light emitting diodes and high-power electronics, because of its unique physical-chemical properties including high hardness, high melting point, excellent thermal conductivity, and wide bandgap. In recent years, its color centers have also been used as potential sources of single photons. Given that borides and carbides are refractory materials, we decided to study a heterostructure formed by an n-doped silicon carbide substrate and a layer of tantalum monoboride (TaB) for near ultraviolet (UV) photodetection. It is shown that the addition of TaB creates a rectifying device that can handle currents higher than 300 mA, showing its potential for high-power optoelectronic devices. The detector also has a high responsivity of 2.9 A/W at the free-space wavelength of 405 nm and a fast frequency response of 610 kHz. The high performance of the detector is attributed to the high thermal and electrical conductivity, large bandgap of SiC, and its moderately close match in atomic arrangement with TaB. Such heterostructure offers a simple method to produce high-performance near UV photodetectors operating under hard conditions such as high power, high temperature and work in corrosive or oxidizing environments.

Exemplar-Guided Sedimentary Facies Modeling for Bridging Pattern Controllability Gap

Inferring subsurface structure from sparse log data is crucial for geology. Recently, deep-learning-based methods, which provide sufficient prior knowledge from training sets, have been proven to aid in sedimentary facies modeling. However, these methods suffer from suboptimal controllability of the geological model, i.e., the expected geological pattern fails to be specified, resulting in unpredictable generated geological structures. To bridge the gap, we propose a novel Exemplar-Guided Facies Modeling (EGFM) approach, which synthesizes a facies model from log data given a pattern exemplar. The key insight in EGFM is to decouple the content and pattern in the target model, where the content refers to the match with well data, and the pattern is the properties of geological structures, such as fluvial course and shape. On the basis of well data as the hard condition, a pattern exemplar is introduced as the reference model for geological realizations. In addition to preserving the commonalities of the holistic geological pattern (from the geological image set), such as structural connectivity, the pattern details of the geological realization can be tuned through pattern exemplars. Moreover, we introduce an adaptive feature fusion block (AFB) to adaptively fuse the content and pattern features for more natural results. Extensive experimental results on two river data sets demonstrate that our proposed EGFM for conditional facies modeling achieves satisfying visual quality and pattern controllability.

IMPROVED ADAPTIVE NONLINEAR CONTROL FOR VARIABLE SPEED WIND-TURBINE FED BY DIRECT MATRIX CONVERTER

This paper proposes a robust decoupling power algorithm based on a doubly fed induction generator (DFIG) for variable speed wind-turbine (WT). The DFIG rotor circuit is fed by the direct matrix converter (DMC), which presents several features such as no need to the dc-bus voltage, sinusoidal supply, rotor side waveforms, bidirectional power flow, and adjustable input power factor. The 18 bidirectional switches are controlled using the Venturini modulation technique. On the other hand, the DFIG stator circuit is connected directly to the grid. The nonlinear control strategy based on feedback linearization is applied to control the stator power (Ps and Qs) independently using the rotor quadrature and direct currents (irq and ird), which present the images of the previous stator powers. Some limitations appear in the power algorithm using the conventional pi controller, especially in power tracking, error, and quality. In this context, the model reference adaptive controller (MRAC) presents an alternative solution, a robust and efficient controller proposed instead of the pi controllers to control stator powers. Finally, the simulation results confirm that the proposed algorithm could work under hard conditions and demonstrate that the wind energy conversion system (WECS) provides enhanced dynamic responses in transient and steady states and good power quality delivered to the grid.

Первые женщины-врачи на службе Саратовского земства (конец XIX – начало XX в.)

Introduction. The gender aspects of modern medicine determine the research interest in the activities of the first female doctors in Russia. In contrast to private practice, the work of doctors in the zemstvo played an important social role. Therefore, the object of this study is the activities of the first female doctors in the service of the Saratov zemstvo. Methods and materials. The source base of the study was the materials of the zemstvo periodicals and office-work documentation (journals of zemstvo meetings, reports of councils, protocols of medical congresses). The historical-systemic method made it possible to consider the professional activities of the first female doctors of the Saratov zemstvo in the context of the formation of the system of women’s medical education in the Russian Empire. With the help of the historical-comparative method, the general features of the professional activity of V.I. Bukhovtseva, A.I. Sukhodeeva, and E.A. Kharizomenova were defined. Analysis and results. The authors established the first female doctors appeared in the service of the Saratov zemstvo at the turn of the 1880–1890s. The entry of women into the zemstvo service was hampered by restrictions on the independent medical practice, the termination of medical courses in 1887, and hard working conditions in the Russian provinces. However, the activities of V.I. Bukhovtseva, A.I. Sukhodeeva and E.A. Kharizomenova at the Saratov zemstvo demonstrated the organizational and research abilities of the first female doctors, their awareness of the medical and social problems of the Russian hinterland, and active participation in sanitary and educational work. Restoration and development of higher medical education for women at the turn of the 1890–1900s became the main factor in the increase in the number of female doctors in the zemstvo service, the expansion of their professional competencies, and the increased role in the development of the health care system. Authors’ contributions. The study of zemstvo office documentation and periodicals containing information about the activities of the first female doctors in the Saratov province was carried out by Candidate of Historical Sciences, associate professor O.S. Kitsenko. Information about the number and place of service of female doctors in the Russian medical lists of 1883–1916 analyzed by the Candidate of Philosophical Sciences, associate professor R.N. Kitsenko.

Experimental and Simulation Study on the Hard Rock–Breaking Characteristics of Disk Cutter under the Water Jet Precutting Kerf

The effect of water jet kerf depth (H) and cut spacing (S) on the rock-breaking performance of a disc cutter under water jet precutting kerf was investigated through a full-scale linear cutting test and numerical analysis with a discrete element method (DEM). Rock-breaking force, rock chip, and rock-breaking efficiency are used to evaluate the rock-breaking performance. The rock-breaking experimental results show that the rock failure patterns are closely related to H and S, and distinct rock failure patterns are shown for the different rock-breaking parameters. In addition, this study reveals the variation law of rock-breaking force and specific energy (SE) consumption with H and S. The difference in crack expansion between rock-breaking under conventional and precutting kerf conditions was compared with numerical simulations. The lateral cracks tend to expand toward the bottom of the precutting kerf and are more prone to produce large-sized rock chips in the precutting kerf condition. In addition, the increased H promotes the expansion of the vertical and lateral cracks, which resulted in different rock failure patterns. Therefore, the numerical, and experimental results show that the rock-breaking of the disc cutter under the precutting kerf conditions is promising, which significantly improves the rock-breaking performance of the disc cutter in hard rock conditions.