Back Row Research Articles

Assessment of airborne transmitted infection risk in classrooms using computational fluid dynamics and machine learning-based surrogate modeling

In recent years, the assessment of airborne transmitted infection risk has been extensively performed using Computational Fluid Dynamics (CFD) simulations, especially in response to the COVID-19 pandemic. Nevertheless, the high computational demands and time-intensive nature of CFD simulations highlight the need for fast or real-time infection risk predictions. This capability is crucial for swift decision-making in dynamic environments where timely health interventions are critical. This paper presents a thorough analysis of airborne infection risks in classroom environments based on CFD simulations to understand key factors such as ventilation strategies, air change rates, occupant arrangements, source locations, and particle sizes. This study also employs data-driven supervised learning methods—specifically, Long Short-Term Memory (LSTM) and Artificial Neural Networks (ANN)—to generate surrogate models for predicting airborne infection risk. Key findings reveal that different ventilation strategies significantly affect airborne infection risk, reducing it by 49 %–77 %. Moreover, the conventional Wells-Riley model was identified as lacking in its ability to accurately predict local infection risks. The study further challenges the assumption that higher air change rates are universally beneficial, considering that occupants seated in the back rows of a classroom experienced up to a 166 % increased risk, despite elevating air change rates from 1.1 h−1 to 11 h−1. These results suggest that physical distancing alone may be insufficient and highlight the importance of considering other factors such as occupant arrangements. Regarding the model performance, the ANN-based surrogate model demonstrated varying prediction accuracy. For inhalable particle concentration predictions for susceptible occupants, R2 values ranged from 0.31 to 0.65 with CVRMSE values between 100 % and 180 %. In contrast, the model achieved an R2 of 0.79 and a CVRMSE of 34 % for infectors. The insights and methodologies from this study can inform HVAC system design and operation strategies to better mitigate infectious disease transmission in densely occupied indoor environments.

The Incidence and Propensity of Head Acceleration Events in a Season of Men’s and Women’s English Elite-Level Club Rugby Union Matches

ObjectivesTo describe and compare the incidence and propensity of head acceleration events (HAEs) using instrumented mouthguards (iMG) by playing position in a season of English elite-level men’s and women’s rugby union matches.MethodsiMG data were collected for 255 men and 133 women from 1,865 and 807 player-matches, respectively, and synchronised to video-coded match footage. Head peak resultant linear acceleration (PLA) and peak resultant angular acceleration (PAA) were extracted from each HAE. Mean incidence and propensity values were calculated across different recording thresholds for forwards and backs in addition to positional groups (front row, second row, back row, half backs, centres, back three) with 95% confidence intervals (CI) estimated. Significance was determined based on 95% CI not overlapping across recording thresholds.ResultsFor both men and women, HAE incidence was twice as high for forwards than backs across the majority of recording thresholds. HAE incidence and propensity were significantly lower in the women’s game compared to the men’s game. Back-row and front-row players had the highest incidence across all HAE thresholds for men’s forwards, while women’s forward positional groups and men’s and women’s back positional groups were similar. Tackles and carries exhibited a greater propensity to result in HAE for forward positional groups and the back three in the men’s game, and back row in the women’s game.ConclusionThese data offer valuable benchmark and comparative data for future research, HAE mitigation strategies, and management of HAE exposure in elite rugby players. Positional-specific differences in HAE incidence and propensity should be considered in future mitigation strategies.

The association of the ACE gene I/D polymorphism and in-game performance in elite Rugby Union players

Genetic variation has been proposed as a factor in human athletic performance. The angiotensin converting enzyme (ACE) gene has been studied extensively albeit with heterogeneous results. The insertion (I) and deletion (D) alleles have been associated with altered serum and tissue ACE, as well as endurance- and power-based performance respectively. It is suggested the distinction in rugby union performance can be partly attributed to variations in the ACE gene. The aim of this study was to identify associations between the ACE I/D genetic polymorphism and in-game performance in elite (≥ 5 games at top-flight) rugby union athletes. The athlete cohort consisted of 347 Caucasian men, divided into positional groups (backs and forwards) and positional subgroups (front five, back row, halves, centres, and back three). Ethical approval was provided by Manchester Metropolitan University with written informed consent obtained from all participants. Genotyping and genotype analysis was performed using a combination of the X9 High-Throughput Genomics System (Standard BioTools) and the StepOnePlus™ Real-Time PCR System (Applied Biosystems) and their respective corresponding software. IBM SPSS Statistics 28 (SPSS, Chicago, IL) software was used to conduct Pearson's Chi-square (χ2) test of independence comparing genotype and allelic frequencies and the Kruskal-Wallis H and Mann-Whitney U tests to investigate differences between genotypes. Genotypic and allelic frequencies did not differ at the population level, nor at the positional group/subgroup levels. Performance did not differ between genotypes nor alleles at the population and positional group levels. Back row II genotypes beat more defenders than IDs (P = 0.008) but completed fewer tackles than both IDs (P = 0.05) and DDs (P = 0.013). Halfback DDs missed fewer tackles than both IDs (P = 0.003) and IIs (P = 0.01). Centre DD genotypes made more carries than IIs (P = 0.006). Back three IIs scored more tries than both IDs (P = 0.005) and DDs (P = 0.007) and made more clean breaks than IDs (P = 0.004). Most of the existing literature has been concerned with identifying the ACE gene as a marker of elite performance. To our knowledge, this is the first study to elucidate how the inter-personal differences in rugby union performance are influenced by the ACE I/D polymorphism. The findings from this study may provide novel insight into the specialisation of training and rehabilitation modalities for athletes, based on their genetic makeup.

Estimation of The Maximum Bending Moment on Pile Group Under One-Way Cyclic Loading in Sandy Soil

In fact, most civil engineering projects are subjected to cyclic loads. The sources of this load are usually seismic, wind, sea waves, and others. Model tests in sandy soil were performed to determine the maximum bending moment at which a pile group (2x2) would respond under one-way lateral cyclic loading. The group pile was made of aluminum piles that were installed in sandy soil with a 70% relative density and three-pile spacing of (3D, 5D, and 7D). The cyclic loads ratio (CLR) used are (0.6, 0,0,8, and 1.0) that is a result from average lateral static load. It can be concluded that an increase in group pile spacing can reduce the maximum bending moment by up to 92%. In addition, As the distance increases, the bending moment decreases, the front pile group provides a greater maximum bending moment than the back rows, as the maximum value in comparison reached 53%.

Numerical study on lead–bismuth cross-flow induced vibration in the elastic tube bundle

The physical properties of liquid lead–bismuth eutectic fluid are quite different from that of water or air. It needs to be verified whether the cross-flow vibration mechanism and the empirical prediction model of fluidelastic instability in conventional media are applicable to lead–bismuth. In this work, for an in-line elastic tube bundle with pitch ratio P/D = 1.5, the flow excitation of lead–bismuth at 200 °C is studied and compared with that of water in uncoupled flow field. Then, two cases of lead–bismuth flow-induced vibration with different mass-damping parameters are simulated and studied by fully coupled numerical simulation considering fluid viscous damping. The tube bundle experiences the process from turbulence-induced vibration in low flow velocity to fluidelastic instability in high velocity. The results of flow excitation show that the pressure coefficient distribution of the front row tube in lead–bismuth is basically consistent with that in water, while the inconsistency of the pressure coefficient distribution for the back row tube is caused by the bi-stable deflective flow. The results of lead–bismuth flow-induced vibration show that, in fluidelastic instability, the vibration of tube bundle and the vortex shed from tube bundle are dominated by the frequency close to the first wet modal frequency of tube bundle. The different deflective directions of lead–bismuth and water, caused by bi-stable characters, have less effect on the onset of fluidelastic instability. The instability points of lead–bismuth agree with the experimental results of other media and the Connors prediction model considering fluid viscous damping. The prediction model is suggested to predict the onset of fluidelastic instability induced by lead–bismuth cross-flow in the tube bundle.

ЧИСЛО ГЛАСНЫХ В УЗБЕКСКОМ И ТУРКМАНСКИХ ДИАЛЕКТАХ ХОРЕЗМСКОЙ ДИАЛЕКТНОЙ ЗОНЫ

People who speak the Uzbek dialects of Oghuz and Kipchak, as well as Kazakh, Karakalpak, and Turkmen, live in the Khorezm dialectal zone, which is a component of the Turkic linguistic region and of the Uzbek language massif. The Oghuz group of Turkic languages, which historically include Uzbek and Turkmen, has both similarities and differences. Phonetics, particularly the vowel system, shows these similarities and contrasts. The Old Turkic language's phonological structure is known to have 8 vowel phonemes. Due to historical growth, impact from related and unrelated languages (metization and hybridization), and different vocalisms, these languages have different levels of retention of shared elements. Research has demonstrated the presence of Tajik components in these dialects as well as Uzbek elements in the Tajik language as a result of the close and ongoing contact between urban and city-type dialects of the Uzbek language and the Tajik language. The Oghuz dialects of Uzbek and Turkmen, who traditionally inhabited in the same region, have distinctive qualities that set them apart from other Uzbek and Turkmen language dialects and make them exclusive to this region. The back row, semi-labial, low-wide vowel ā ,for instance, started to be actively utilized in the Uzbek dialects of the dialectal zone under the influence of the Uzbek literary language ,like ālíj, āmmavíj. In the zone's Turkmen languages, this vowel ,therefore ,started to occur irregular. The article offers details on the typical indications of vowel sounds in Uzbek and Turkmen, two languages spoken in the region, according to the sign of quality.

Communication Apprehension among the Communication Students of Bangladesh

The aim of this study is to assess the communication apprehension (CA) among the communication students of Bangladesh. The data were collected from 283 students from 10 public universities through the survey method. McCroskey's (1982) Personal Report of Communication Apprehension, also known as the PRCA-24 test was adopted for this study. The data were analyzed using both descriptive and inferential statistics of SPSS 23 software. The study explores that the mean communication apprehension score of communication students of Bangladesh is 68.12 which ascertains the medium level of CA of the students. It also says that 12.6% of students have high CA, 64.7% have medium CA and the rest 13.8% have a low level of communication apprehension. Students are more apprehensive in public communication rather than in group, meeting, and interpersonal communication. Male students have less CA than female students. This research also reveals that those students experience more CA who suffer from depression, prefer loneliness, and spend more time on social media. Communication apprehensive students prefer to sit in the back row or alongside in the classroom setting. Also, CA score is decreased when the age of the student is increased. The study also assesses that students involved with co-curricular activities have less CA than the other students. The study recommends that universities should offer more practical courses in communication to overcome communication apprehension. Keywords: communication, apprehension, communication students, Bangladesh, university students

Study of the Effect Developed Chisel Plow on some Soil Properties in Heavy, Clay-Textured Soils

A field experiment conducted in the fields of the College of Agriculture - University of Basrah, Karmat Campus, according to the randomized complete block design (RCBD), to study the effect of height sweeps shank in back row with the developed chisel plow (10 and 20 cm), with three depths (15, 25 and 35 cm) and three lateral distances (20, 25 and 30 cm), on the field performance indicators where the mean weighted diameter, bulk density and total soil porosity are present. In mixed loamy soil with a density of (1.25) g cm3 and a moisture content of (15.17)%, the experiment was designed according to the randomized complete block design (RCBD). The results showed that the improved chisel plow was significantly superior to the normal chisel plow by giving it the lowest mean weighted diameter ratio (higher fracturing), the least density, and the highest porosity, as the weighted diameter decreased significantly when both the lateral distance and the height of sweeps shank increased. The values of the mean weighted diameter (increased smoothing) decreased at a height of 20 cm of sweeps shank, and increased with the increase in lateral distance and depth. Bulk density values decreased at 10 cm height for the rear sweeps shank, and increased with increasing the lateral distance and the depth of plowing. The porosity increased at the height of the sweeps shank 10 cm and the depth of tillage 15 cm, and there was no significant effect of the lateral distance in the porosity.

Differences is students' performance, (mis)calibration, and confidence judgments depending on their preferred sitting position in class

Students who perform better academically are generally more accurate in assessing their performance. In other words, they are better calibrated, showing smaller discrepancy between their predicted and actual performance. Research into contextual variables related to performance has shown that students sitting position may be related to their performance in class. In the current study we attempted to bring several lines of research together and examine whether there are differences in academic performance, calibration, and confidence judgments among students who choose various sitting positions in the classroom.130 college students (M = 21.52, SD = 1.59; 103 female) attending courses at the University of Jaen in Spain participated. Results revealed that students' calibration differed depending on their preferred sitting position. We found that students in middle rows were optimally calibrated, students in the front rows overestimated their performance, and those in the back rows tended to underestimate their performance. Furthermore, students in the front rows were the most confident in their estimates, whereas students in the middle and back rows were less confident, suggesting the manifestation of the Dunning-Kruger effect. Future directions for contextual variables contributing to students' optimal calibration are discussed.

Basin testing of the 1-2-1 M4 WEC

The M4 family of Wave Energy Converters consist of 3 rows of floats, with the front two rows rigidly connected and a hinged connection(s) to the back row. The various possible configurations are commonly identified by the number of floats in each row – hence 1-2-1 has 1 float in front, 2 in the middle, and 1 at the rear. A study by Stansby et al 2017 [1] showed that the 1-2-1 and 1-3-2 variants had the lowest cost of energy of all configurations studied. The 1-3-2 variant has subsequently been extensively studied as it provides greater power per machine. However, the 1-2-1 machine has received less attention. In this paper we report, for the first time, wave basin testing of a 1-2-1 variant. The design is a 1:15 scaled version of a 1-2-1 M4 suitable for deployment in the prevailing short period wind waves in King George Sound, Albany, on the south coast of Western Australia. 
 
 The tests were carried out in the Model Test Basin at the Australian Maritime College, Tasmania. This basin is 35 m x 12 m and tests were run with a water depth of 0.8 m. For modelling operational conditions, the power take-off was represented by a pneumatic ram; in extreme seas the power take-off was removed.
 
 Decay tests, irregular operational seas and irregular extreme seas were tested. All waves were long crested. Sea states tested were taken from the scatter diagram for the deployment site in King George Sound. Body displacements, mooring loads, run-up on the middle floats and forces in the PTO (where installed) were measured. Measured motions and power were compared to a linear model. The level of agreement is compared with previous tests on other variants of M4 in the published literature, including the 1-3-2 variant tested in Carpintero-Moreno et al [2] and the 1-1-1 variant tested in Stansby et al [3]. Compared to some other configurations (such as 1-3-2) the 1-2-1 M4 is more prone to roll. Implications of the test results for deployment in King George Sound are discussed.
 
 [1] Stansby, P., Moreno, E.C. and Stallard, T., 2017. Large capacity multi-float configurations for the wave energy converter M4 using a time-domain linear diffraction model. Applied Ocean Research, 68, pp.53-64.
 
 [2] Carpintero-Moreno, E. and Stansby, P., 2019. The 6-float wave energy converter M4: Ocean basin tests giving capture width, response and energy yield for several sites. Renewable and Sustainable Energy Reviews, 104, pp.307-318.
 
 [3] Stansby, P., Moreno, E.C. and Stallard, T., 2015. Capture width of the three-float multi-mode multi-resonance broadband wave energy line absorber M4 from laboratory studies with irregular waves of different spectral shape and directional spread. Journal of Ocean Engineering and Marine Energy, 1, pp.287-298.

Numerical Simulation and Field Test of a PDC Bit with Mixed Cutter Arrangement to Break Non-Homogeneous Granite

As the depth of petroleum drilling increases, the strata environment becomes more complex. The efficiency and lifespan of Polycrystalline Diamond Compact (PDC) drill bits fail to meet current drilling demands. However, the structure and arrangement of PDC cutters are valuable determinants of drilling efficiency, although related research still has gaps and deficiencies. This study focuses on PDC cutters in axe, triangular prism, and circular forms. It establishes an inhomogeneous granite model based on the actual measurements of granite and verifies the accuracy of this model through uniaxial compression simulation. Finite element models of three types of cutters in various combination schemes are constructed to examine rock-breaking effects, with the best scheme optimized using Box-Behnken response surface methodology. The rock-breaking process of the optimal PDC drill bit layout has been compared to that of a single cutter bit. Field drilling has demonstrated the effectiveness of a mixed cutter arrangement. The results show that the inhomogeneous granite model can be trusted. The optimal arrangement involves axe cutters in the front row and an alternate arrangement of triangular prism cutters and axe cutters in the back row. The optimal lateral and longitudinal distances for the triangular cutters from the front row of axe cutters are 10 mm and 7 mm, respectively, while those for the back row of axe cutters from the front row are 10.06 mm and 7 mm, respectively. The ROP standard deviation in the drilling process of mixed cutter bits decreases by 53.06% and 43.08% compared to axe and triangular prism cutter bits, respectively. The drilling efficiency increases by 16.8% and 16.6%, respectively, demonstrating higher efficiency and stability. Field drilling results indicate that a mixed cutter bit increases efficiency by 23.5% compared to a bit with only triangular prism cutters. This study posits that research on the combination schemes and parameters of PDC cutters can significantly enhance drilling efficiency, thereby reducing the drilling cycle and costs.

NDMFCS: An automatic fruit counting system in modern apple orchard using abatement of abnormal fruit detection

Automatic fruit counting is an important task for growers to estimate yield and manage orchards. Although many deep-learning-based fruit detection algorithms have been developed to improve performance of automatic fruit counting systems, abnormal fruit detection has often been caused by these algorithms detecting non-target fruits that have similar growth characteristics to target fruits. For abnormal fruit detection, detected fruits in the back row of the tree were defined as DFBRT, while detected fruits on the ground were defined as DFG. Both of them would result in a higher number of fruits counting than the ground truth. This study proposes an automatic fruit counting system called NDMFCS (Normal Detection Matched Fruit Counting System) to solve this problem for improving fruit counting accuracy in modern apple orchard. NDMFCS consists of three sub-systems, i.e. object detection based on You Only Look Once Version 4-tiny (YOLOv4-tiny), abatement of abnormal fruit detection based on threshold, and fruit counting based on trunk tracking and identity document (ID) assignment. YOLOv4-tiny was selected to implement detection of fruits and trunks, whose output is confidence and pixel coordinates of detected object. The DFBRT and DFG were abated by thresholds to improve detection performance of fruit. This meant that detected fruits were removed when their distance from camera is further than a distance threshold or the confidence of fruit detection is less than a confidence threshold. Finally, fruit counting was implemented by trunk tracking and ID assignment, where each fruit was assigned a unique tracking ID. Results on 10 sets of original videos indicated that average fruit detection precision was improved from 89.1% to 93.3% after abatement of abnormal fruit detection. Also, Multiple Object Tracking Accuracy and Multiple Object Tracking Precision were improved on average by 4.2% and 3.3%, respectively, while average ID Switch Rate was decreased on average by 1.1%. And average fruit counting accuracy was improved to 95.0% by 4.2%. Coefficient of determination (R2) was 0.97, which indicated the number of fruits counted by NDMFCS was near to the ground truth. These results demonstrate that the abatement of abnormal fruit detection can improve performance of apple counting, which has the potential to provide a technical support for estimating fruit yield in modern apple orchards.

Analysis of Influence Factors of Anti-Slide Pile with Prestressed Anchor Cable Based on Bearing and Deformation Characteristics of Pile Body

In order to deeply study the mechanism of prestressed anchor anti-slide pile, an indoor model experimental device was developed, and a finite difference and particle flow numerical analysis model of slope anchor cable anti-slide pile was established based on the reinforcement project of prestressed anchor cable anti-slide pile in a mountain road slope. Based on the analysis of the force and displacement characteristics of the anti-slide pile, the influence of the prestress of the anchor cable, the inclination angle of the anchor cable, the width and column spacing of the anti-slide pile and the inclination angle of the landslide, the height and nature of the filling soil on the force and deformation characteristics of the pile are discussed, and some design parameters are optimized. Results show that the larger the prestress of the anchor cable, the smaller the displacement of the pile body, but the excessive stress is not conducive to the safety of the pile body. The optimal tension should be 50–70% of the designed tension of the anchor cable. With the increase in the inclination angle of the anchor cable, the displacement of the pile decreases first and then increases, and there is an optimal inclination angle of the anchor cable. In the double row piles, with the increase in pile spacing, the front row piles gradually change from supporting the soil between the double row piles to supporting the sliding body with the back row piles, and the double row piles are plum-shaped. When the pile spacing is 2.5 times the pile diameter, the force of the front and rear piles is the most reasonable. In the process of soil arching evolution, the influence of cohesion on the soil arching effect is greater than that of the internal friction angle.

Robust cabbage recognition and automatic harvesting under environmental changes

In Japanese agriculture, labor shortages are becoming increasingly severe due to the lack of farmers and aging. Therefore, extensive research has been conducted on the automation of cabbage harvesting. In automatic cabbage harvesting, cabbage detection is performed using deep learning. In the evening hours, if the backlight enters the camera, cabbage detection is not possible. Moreover, cabbages in the back row that are not to be harvested are detected and targeted for harvest. To solve these problems, we have proposed new recognition methods in this paper. We performed cabbage detection using the lower half of the cabbage and performed cabbage selection using an RGB-D camera. Moreover, sliding-mode control was incorporated to enable automatic harvesting in the soft soil. The experimental results demonstrate the effectiveness of these proposed methods.

Case Study on the Effect of Delay-Time Differences between Columns during Blasting Demolition of RC Structures with a Small Height-to-Width Ratio

Blasting demolition plays an important role in building demolition, and numerical-simulation methods can facilitate the optimization of blasting-demolition schemes. To study the influence of the delay-time differences between columns on the blasting and demolition effect of small-aspect-ratio reinforced concrete structures, a separated common node model of small-aspect-ratio structures was established through the finite element numerical simulation software ANSYS/LS-DYNA. The results showed that the delay-time differences between columns influenced the position of the plastic hinge of the structure, and the plastic hinge was located at the end of the back span beam when the delay-time difference was 0.1~0.3 s. The plastic hinge moves to the top of the back row of the columns of the first floor at 0.4~0.8 s and to the end of each span of the beams at 0.9 s. When the plastic hinge is at the end of the beam, the orientation axis is located at the bottom of the back row of the columns of the first floor. Moreover, when the plastic hinge is at the top of the back row of the columns of the first floor, the orientation axis is at the same position as the plastic hinge. The delay-time difference also affects the recoil distance of the structure as well as the height of the burst pile. To ensure that the structure can be successfully collapsed under the preconditions of disintegration, for a small height-to-width ratio structure, the appropriate intercolumn delay-time difference is 0.4~0.5 s.

On being entirely ordinary

On being entirely ordinary

Running demands in club, regional, national, and international provincial New Zealand rugby union competitions.

The demands of national and international professional rugby union matches are well established, however, there has not been a comparative study investigating running demands in New Zealand teams playing in club (amateur), Heartland Championship (semi-professional Div 2), the Mitre 10 Cup (semi-professional Div 1) or Super Rugby (professional) competitions. This information could enable specific training and rehabilitation that programmes to be developed to meet the needs of players in the different competitions. Players wore 10 Hz GPS units during games for one rugby season to determine absolute (m) and relative (m.min-1) measures for total distance, running volume (∼≥7 km·h-1) and high intensity running (∼≥16 km·h-1). There were typically minimal differences (1-2 m.min-1) in running distance measures between amateur level front row forwards and inside backs compared to players in these positions at higher levels of competition. Therefore, amateur players in these positions may find the transition to higher competitions less challenging with respect to running load. In contrast, amateur outside backs and back row forwards may find the increased pace of higher levels of competition more challenging due to typically covering significantly less running and high intensity running distances in amateur games. Differences for half backs were more variable between the levels of competition. Based on our results, it cannot be assumed that amateur rugby has lower running demands than higher competitions or that there is a continuum of increased running demands with increasing competition levels, as some playing positions in the semi-professional (Div 2) (second lowest level of competition) team recorded the largest values for total distance, running and high intensity running. Therefore, the specificity of running demands in a position and competition need to be considered individually for each player when transitioning between competitions. The practice and perception of returning a professional player to amateur club rugby due to the belief that running loads being lower may also be flawed, as we found considerable positional variation in running demands within-and-between competitions.

What I Think about When I Think about Teaching Ethics: A Philosophical Exploration in Pedagogy

What I Think about When I Think about Teaching Ethics: A Philosophical Exploration in Pedagogy

A Method for Evaluating the Rock Breaking Efficiency of Cutters and Optimizing the PDC Cutter Profile—A Study of Igneous Rock Formations in Shunbei Oilfield

The Permian igneous rock in Shunbei Oilfield exhibits high rock strength, which results in a low rate of penetration (ROP) and shortens the cutter’s service life. It is necessary to analyze and evaluate the rock breaking effect of cutters. However, at this stage, the evaluation of the rock breaking effect has been limited to comparing the sizes of the mechanical specific energy (MSE), and the change in the rock breaking efficiency caused by the difference in the shape of the cutters’ surface has not been considered. Therefore, through the establishment of numerical simulation models of a circular cutter, bevel cutter, axe cutter, wedge cutter, and triangular cutter, the evaluation of the rock breaking efficiency of special-shaped cutters was completed. The results show that the triangular cutter and the wedge cutter are suitable for the front row cutter of the polycrystalline diamond compact bit (PDC); the triangular cutter is suitable for drilling into medium–hard formations, the wedge cutter is suitable for drilling into hard formations, and the bevel cutter is suitable for the back row cutter of the PDC, to assist other cutters in the process of rock breaking. The research results can provide the basis for the selection of PDC bit cutters and the design optimization of the bit.

Attack by a Turkey: Learning to Write History from Bernard Bailyn

Attack by a Turkey: Learning to Write History from Bernard Bailyn