Large Diameter Research Articles

Динамика анатомических и функциональных показателей после хирургии сквозных макулярных разрывов большого диаметра

Full-thickness macular hole (FTMH) is the macular zone pathology, leading to a significant decrease in visual acuity. According to the literature, classical surgery of FTMH allows to achieve anatomical closure only in 73.3 % of cases. The task of developing a method of surgical treatment of FTMH with the possibility of evaluating its closure intraoperatively is relevant and of strategically important interest for the development of ophthalmic surgery. The purpose of this study is to evaluate the dynamics of functional and anatomical results of large diameter FTMH surgery. Material and methods. A randomized study was conducted on two comparable groups of patients. Surgical treatment of FTMH was performed in both groups, the difference was in the FTMH closure method: in the first group, treatment was carried out according to the proposed method, in the second group, autologous conditioned plasma was used during the surgery. Patients underwent a standard ophthalmological examination, as well as optical coherence tomography of the retina before surgery, 1, 3 and 6 months after surgery. Results and discussion. In the control group, 4 cases of FTMH recurrence were recorded in the postoperative period up to 1 month after surgery. U-shaped closure pattern (Fig. 1) was more often observed in the first group, while in the second group V-shaped closure pattern was more often observed (Fig. 2). Visual acuity 6 months after surgery was higher on average in patients in the first group (p = 0,05). Conclusions. The results obtained indicate a decrease in the risk of recurrence of FTMH, as well as higher visual acuity and close-to-normal retinal histological state in the postoperative period for a period of 6 months when closing the FTMH according to the proposed method. The use of the FTMH closure method under the intraoperative optical coherence tomography control makes it possible to minimize the time of the patient's forced position in the postoperative period, which facilitates its course. Keywords: vitreoretinal surgery, macular hole, optical coherence tomography, autologous conditioned plasma

Numerical and experimental investigation of the effect of radiant reflector on the conical solar collector for heat transfer enhancement

Solar energy is a widely available and renewable form of energy, offering a promising alternative to fossil fuels. Various methods exist for harnessing solar energy, and one common approach involves the use of solar collectors. However, ongoing research aims to develop new and more efficient collectors. This study focuses on designing a conical solar collector and evaluating its performance based on the ASHRAE standard. The objective is to achieve superior efficiency compared to other collectors in the field. Due to experimental limitations, the optimal geometry of the conical solar collector was determined through numerical modeling. The most effective collector design identified had a small diameter of 58 mm, a large diameter of 336 mm, a height of 146 mm, and featured 12.67 turns. Subsequently, the selected model was subjected to laboratory testing. The results demonstrated that the highest efficiency was attained by incorporating a reflector and maintaining a flow rate of 1.5 l/min, resulting in an efficiency exceeding 81%.

Towards the preparation of single-walled carbon nanotubes with average diameter of 1.2 nm

Preparation of single-walled carbon nanotubes (SWNTs) with diameters ranging from 1.2 to 1.5 nm has been highly demanded for field-effect transistors with superior properties. In the work, we report the chemical vapor deposition synthesis of SWNTs with an average diameter of 1.2 nm from a rationally designed nickel catalyst supported by magnesia. The high metal dispersion, the suitable reaction temperature, and the use of a methane carbon source co-determine the SWNT diameter distribution. Furthermore, through the synergistic application of poly(9,9-dioctylfluorene-2,7-diylalt-pyridine-2,6-diyl) wrapping and ultracentrifugation, SWNTs with enriched (10,8) species of 1.24 nm are successfully extracted, which is attributed to the selective interaction between the polymer molecules and the targeted SWNTs. This work not only sheds light on the growth of SWNTs with relatively large diameter, but also paves the way towards the preparation of high purity (n,m) species that could meet the requirements of advanced high-tech applications.

Whole Genome Sequencing Highlights the Pathogenic Profile in Nocardia Keratitis.

Nocardia keratitis is a serious and sight-threatening condition. This study aims to reveal the virulence and antimicrobial resistance gene profile of Nocardia strains using whole genome sequencing. Whole-genome sequencing was performed on 23 cornea-derived Nocardia strains. Together with genomic data from the respiratory tract and the environment, 141 genomes were then utilized for phylogenetic and pan-genome analyses, followed by virulence and antibiotic resistance analysis. The correlations between virulence genes and pathogenicity were experimentally validated, including the characteristics of Nocardia colonies and clinical and histopathological evaluations of Nocardia keratitis mice models. Whole-genome sequencing of 141 Nocardia strains revealed a mean of 220 virulence genes contributed to bacterial pathogenesis. The mce gene family analysis led to the categorization of strains from the cornea into groups A, B, and C. The colonies of groupC had the largest diameter, height, and fastest growth rate. The size of corneal ulcers and the clinical scores showed a significant increase in mouse models induced by groupC. The relative expression levels of pro-inflammatory cytokines (CD4, IFN-γ, IL-6Rα, and TNF-α) in the lesion area exhibited an increasing trend from groupA to groupC. Antibiotic resistance genes (ARGs) spanned nine distinct drug classes, four resistance mechanisms, and seven primary antimicrobial resistance gene families. Whole genome sequencing highlights the pathogenic role of mce gene family in Nocardia keratitis. Its distribution pattern may contribute to the distinct characteristics of the growth of Nocardia colonies and the clinical severity of the mice models.

On finite 2-distance-primitive graphs

A vertex-transitive graph is called 2-distance-primitive if the vertex stabilizer is primitive on both the first step and the second step neighborhoods. This paper first shows that there are infinitely many 2-distance-primitive graphs with unbounded large valency and diameter. Then a classification is given of the 2-distance-primitive graphs with valency at most 9. Finally, we determine all the 2-distance-primitive graphs with the order of a product of two primes.

Effect of thermoplastic mask hole diameter on dose distribution in the build-up region of medical LINAC

This study aims to investigate the effect of variations in the hole diameter of unstretched thermoplastic masks offered by a single company on the dose distribution in the build-up region. 2, 2.5, 3 and 4 mm hole diameters masks with the same properties were irradiated with 6 MV X-rays and dose distribution was analyzed according to the open field. Dose measurements were obtained with a parallel plane ionization chamber. All irradiations were repeated for 5 × 5, 8 × 8, 10 × 10 and 15 × 15 cm2 beam fields. It was observed that the mask had a bolus effect in all measurements. It was observed that this bolus effect varied especially depending on the hole diameter in the mask. In a 10 × 10 cm2 field, the dmax depth without mask was 15 mm, while the dmax for masks with 2, 2.5, 3 and 4 mm hole diameters was 11, 12, 13 and 13 mm, respectively. It was observed that the mask hole diameter affected the dmax depth. Thermoplastic masks with large hole diameters increase the surface dose less than those with small hole diameters.

Rapid Prediction of Pile Friction Resistance Based on Soil Deformation Law Caused by a Super Large Diameter Tunnel: A Case Study

Rapid Prediction of Pile Friction Resistance Based on Soil Deformation Law Caused by a Super Large Diameter Tunnel: A Case Study

Effect of crop pattern and types of manure on the growth of Sappan wood (Caesalpinia Sappan L.) in Jatinangor, West Java, Indonesia

Sappan wood plants are one of the medicinal plants in Indonesia. Considering the potential of Sappan wood plants in the health and industrial sectors, special cultivation techniques are required to ensure that Sappan wood plants can grow with a large stem diameter. A large stem diameter can be achieved by using the appropriate planting distance. The right planting distance requires land with sufficient organic content. This research aims to determine the optimum planting distance and the appropriate type of organic material to produce Sappan wood plants with a large diameter. The experimental design used was a Split Plot Design, with planting distance (J) as the main plot and organic fertilizer (P) as the sub-plot. The planting distance factor levels were J1 = 1m x 1m, J2 = 2mx2m cm, J3 = 3m x3m. The organic fertilizer factor levels were P1 = Cow Manure Fertilizer, P2 = Chicken Manure Fertilizer, and P3 = Sheep Manure Fertilizer. The results showed an interaction between the planting distance treatment and the use of manure fertilizer on the parameters of stem diameter and soil pH of Sappan wood plants at 3 MAP (months after planting). The planting distance treatment independently influenced the results, with a 1m x 1m planting distance providing the best results for plant height and stem diameter. In general, the application of different types of manure did not significantly affect the growth of Sappan wood plants.

Research on the cuttings discharge in air cushion chamber of slurry shield based on CFD-DEM coupling method

The rapid discharge of cuttings from the air cushion chamber is crucial for the construction safety and excavation efficiency of the slurry shield. Previous studies have mainly focused on the transport characteristics of cuttings in the slurry discharge pipe, while the complete process of cuttings entering the slurry discharge pipe from the air cushion chamber until they are discharged was often overlooked. Based on the CFD-DEM coupling method and combined with actual engineering, this paper established a numerical model that can more completely reflect the cuttings discharge process during slurry shield tunneling, and the effects of the slurry velocity at slurry gate and scouring pipes, inclination angle of slurry discharge pipe, cuttings diameter and shape coefficient were investigated by analyzing the variation in the mass flow rate, mass of discharged cuttings, and discharged ratio. The results revealed that increasing the slurry velocity can promote the discharge of cuttings. To keep the discharged rate at a high level, it is recommended that the slurry velocity at the slurry gate should be greater than 0.15 m/s. Reducing the inclination angle of the discharge pipe is conducive to the rapid discharge of cuttings. Cuttings with large diameter or small shape coefficient are more prone to accumulate in the air cushion chamber and cause clogging risk. The research results not only help to improve engineers' understanding of cuttings discharge in slurry shield, but also provide practical guidance for formulating relevant construction measures.

Impact of Alcian blue and periodic acid Schiff expression on the prognosis of gastric signet ring cell carcinoma.

The Alcian blue (AB) and periodic acid Schiff (PAS) stains are representative mucus markers in gastric signet ring cell carcinoma (SRCC). They are low-cost special staining methods used to detect acidic mucus and neutral mucus, respectively. However, the clinical importance of the special combined AB and PAS stain is unclear. To investigate AB expression, PAS expression and the AB-to-PAS (A/P) ratio in gastric SRCC patients and to assess patient prognosis. Paraffin-embedded sections from 83 patients with gastric SRCC were stained with AB and PAS, and signet ring cell positivity was assessed quantitatively. Immunohistochemical staining for Ki67, protein 53 (P53) and human epidermal growth factor receptor 2 (HER2) was performed simultaneously. The cancer-specific survival (CSS) rate was estimated via Kaplan-Meier analysis. Cox proportional hazards models were used for univariate and multivariate survival analyses. Kaplan-Meier survival analysis revealed that the 3-year CSS rate was significantly greater in the high-PAS-expression subgroup than in the low-PAS-expression subgroup (P < 0.001). The 3-year CSS rate in the A/P ≤ 0.5 group was significantly greater than that in the A/P > 0.5 group (P = 0.042). Univariate Cox regression analysis revealed that the factors affecting prognosis included tumor diameter, lymph node metastasis, vessel carcinoma embolus, tumor stage, the A/P ratio and the expression of Ki67, P53 and the PAS. Cox multivariate regression analysis confirmed that low PAS expression [hazard ratio (HR) = 3.809, 95% confidence interval (CI): 1.563-9.283, P = 0.003] and large tumor diameter (HR = 2.761, 95%CI: 1.086-7.020, P = 0.033) were independent risk factors for poor prognosis. A/P > 0.5 is potentially a risk factor for prognosis, and low PAS expression is an independent risk factor in the prognosis of gastric SRCC. PAS expression and the A/P ratio could help in predicting the clinical prognosis of patients with SRCC.

The impact of the relationship between lesion diameter and total core length on the detection rate of clinically significant prostate cancer for PI-RADS 3 lesions

BackgroundThe aim of our study was to determine the effect of total core length (TCL) for prostate imaging reporting and data system (PI-RADS) 3 lesions to facilitate clinically significant prostate cancer (csPCa) detection based on the lesion diameter.Materials and methodsA total of 149 patients with at least 1 lesion with a PI-RADS 3 were evaluated retrospectively. The lesions with diameters of < 1 cm were categorized as small lesions and lesions of ≥ 1 cm were categorized as large lesions. The lengths of biopsy cores from PI-RADS 3 lesions were summed for each lesion separately, and TCL was calculated. The relationship between TCL and csPCa was analyzed separately for the small and large groups with multiple logistic regression analyses.ResultsA total of 208 lesions were detected by multiparametric magnetic resonance imaging (MpMRI) in 149 males included in the study. The mean TCL was 44.68 mm (26–92) and the mean lesion diameter was 10.73 mm (4–27) in PIRADS 3 lesions. For small diameter lesions (< 1 cm), the odds of finding clinically insignificant prostate cancer (ciPCa) increase by 1.67 times if TCL increases by one unit. Hence, increasing TCL for small lesions only increases the odds of ciPCa detection. For large diameter lesions (≥ 1 cm), if TCL increases by one unit, the odds of finding ciPCa increase 1.13 times and the odds of finding csPCa increases1.16 times. Accordingly, large lesions are more likely to have both csPCa and ciPCa as TCL increases.ConclusionsOur study showed that for PI-RADS 3 lesions, both more csPCa and more ciPCa were detected as TCL increased. However, in lesions with a size of < 1 cm, only ciPCa was detected more frequently as TCL increased. In conclusion, taking more and longer biopsy cores in PI-RADS 3 lesions below 1 cm does not contribute to the detection of csPCa.

Investigation on shear behavior of large diameter short stud connectors in steel- thin UHPC bridge deck

Ultra-high performance concrete (UHPC) is a promising alternative for improving the mechanical performance of the steel and reinforced concrete composite bridge deck. Because of the excellent compression and tensile strength as well as the superior durability, the thickness of the UHPC slab can be effectively reduced. Therefore, large diameter short headed stud connector was proposed in this study to match the thin UHPC slab. To investigate the shear behavior of the large diameter headed studs in steel-thin UHPC composite bridges, 6 groups of 12 push-out specimens were designed and tested under the static loading. During the test, the failure mode, load-slip curves, the ductility, shear stiffness and shear strength of the specimens were emphatically focused. Besides, the influences of the aspect ratio of the stud, the thickness of the UHPC slab and the number of the stud in one position on shear behavior of the specimens were evaluated. Furthermore, the ABAQUS software has been used to analyse the large diameter short stud. A proposed modelling strategy used for further parametric analysis was validated with the test results. For the parametric research, different aspect ratio of stud and ultimate strength of stud were evaluated. Test and FEM results showed that the specimens failed in the failure of the root of the stud and the crushing of the concrete. With the increasing of the diameter of the stud, the thickness of the UHPC slab and the ultimate strength of stud, the shear strength and the shear stiffness of the specimens increased. Under the same cross-sectional area of the stud, the shear behavior of a single large diameter short stud connector could be comparable to that of two conventional stud connectors. Finally, after evaluating the results obtained from existing formulas, a predictive equation for the shear bearing capacity of large diameter short studs was proposed, and the accuracy of the calculated results was verified.

Nonlinear optical response of strain-mediated gallium arsenide microwire in the near-infrared region

Abstract Gallium arsenide (GaAs) semiconductor wires have emerged as potent candidates for nonlinear optical devices, necessitating bandgap engineering for an expanded operational wavelength range. We report the successful growth of strain-mediated GaAs microwires (MWs) with an average diameter of 1.1 μm. The axial tensile strain in these wires, as measured by X-ray diffraction and Raman scattering, ranges from 1.61 % to 1.95 % and from 1.44 % to 2.03 %, respectively. This strain condition significantly reduces the bandgap of GaAs MWs compared to bulk GaAs, enabling a response wavelength extension up to 1.1 μm. Open aperture Z-scan measurements reveal a nonlinear absorption coefficient of −15.9 cm/MW and a third-order magnetic susceptibility of −2.8 × 10−8 esu at 800 nm for these MWs. I-scan measurements further show that the GaAs saturable absorber has a modulation depth of 7.9 % and a nonsaturation loss of 3.3 % at 1050 nm. In laser applications, GaAs MWs have been effectively used as saturable absorbers for achieving Q-switched and dual-wavelength synchronous mode-locking operations in Yb-bulk lasers. These results not only offer new insights into the use of large diameter semiconductor wires but also expand the potential for applications requiring bandgap tuning.

An Evaluation of Variations in the Carpal Tunnel Dimensions of Adult Subjects in a Hospital-Based Population: An Ultrasonographic Cross-Sectional Study.

Background The carpal tunnel is a groove that spans the palm as a 'U.' The ulnar and radial sides of the wrist are made up of the scaphoid tubercle and trapezium while the palmar aspect is made up of carpal bones. Our study aimed to see whether there were differences in carpal tunnel size between men and women. Material and methods The study was conducted on 65 healthy adults, 13 (20%) were males and 52 (80%) were females (both non-pregnant and pregnant). Inclusion criteria were healthy adults and bilaterally symmetrical limbs. Exclusion criteria were chronic disease, diabetes, hypertension, immunological disorders, any visible abnormalities, and a history of upper extremity pain on either side. A high-resolution ultrasound machine with a linear transducer was used to perform an ultrasound scan of the carpal tunnel. The anteroposterior dimension was measured at the midline, or along the axis of the middle finger, and the transverse diameter was measured at the midpoint of the flexor retinaculum. The cross-sectional area of the tunnel was measured at its largest diameter within the carpal tunnel. All the dimensions were measured in centimeters. Results The mean transverse diameter of the right side was 1.824 ± 0.223 cm (p-value 0.002) and of the left side was 1.742 ± 0.197 cm (p-value 0.004). The mean cross-sectionalarea of the carpal tunnel on the right side was 1.417 ± 0.379 cm2 (p-value 0.008) and on the left side was 1.306 ± 0.303 cm2(p-value 0.004), respectively. Age, sex, weight, and BMI were discussed. The carpal tunnels of females were found to be comparatively squarer and smaller than those of males. Conclusion The transverse diameter and cross-sectional area of the carpal tunnel and their correlation with carpal tunnel syndromeare predicted by age, sex, weight, and BMI. Both sexes had the same wrist ratio.

Bedside preoperative predictors of difficult laryngeal exposure in microlaryngeal surgery.

Successful microlaryngeal surgery relies on an adequate laryngeal exposure. Recognizing the likelihood of challenging exposure prior to microlaryngeal surgery may assist in selecting the appropriate surgical approach and even prompt consideration of alternative treatment options. We aim to apply the mini-Laryngoscore, a preoperative assessment tool, to our study population and incorporate novel variables to optimize the prediction model. This single-center prospective cohort study included 80 consecutive patients undergoing elective microlaryngeal surgery, from January 1, to June 30, 2023. Each patient underwent a presurgical evaluation of 15 parameters and an intraoperative scoring of the anterior commissure visualization. These parameters were assessed for their association with difficult laryngeal exposure, using multiple logistic regression analysis. We created a novel prediction model for DLE and compared it with the existing model, the mini-Laryngoscore. Out of 80 patients, 24 (30%) patients had difficult laryngeal exposure, including 3 cases (3.8%) in which visualization of the anterior commissure was not possible. A large neck diameter (OR, 1.4; CI 1.1-1.9) and the presence of upper teeth (OR, 8.9; CI 1.3-62.8) were independent risk factors for a difficult laryngeal exposure, while a larger interincisors gap was the only independent protector factor (OR, 0.3; CI 0.1-0.8). The logistic regression model combining these three independent risk factors displayed a high discriminative value AUC = 0.89 (CI 0.81-0.97). The predictive performance of the mini-Laryngoscore was 0.73 (CI 0.62-0.85). Combining two parameters from the mini-Laryngoscore (upper jaw dental state and interincisors gap distance) with neck circumference measurement can accurately predict the risk of difficult laryngeal exposure.

Wide-bandwidth mode converter based on a dual-hollow-core anti-resonant fiber

This paper proposes a broadband mode converter utilizing a dual-hollow-core anti-resonant fiber (DHC-ARF) for the first time, in which the mode index matching between LP01 and LP11 modes is achieved by adjusting the core diameter size of the hollow-core anti-resonant fiber (HC-ARF). Notably, the air gap can become the main channel for the energy exchange between the two cores by adjusting the air gap size between the two cores of the DHC-ARF. The coupling length of the mode converter is greatly reduced, and a compact and broadband mode converter is realized. Simulation results demonstrate that the proposed mode converter achieves a coupling efficiency (CE) of 92.79 % at a wavelength of 1.55 μm at a length of 10.7 mm. The bandwidth of 330 nm at a CE greater than 90 % covers the E + S + C + L + U bands. The proposed mode converter exhibits a large core diameter compatible with hollow-core fiber communication and is expected to be applied for high-speed and high-capacity hollow-core mode-division-multiplexing fiber-optic communication. The device design methodology presented in this paper can also provide technical references for developing higher-order mode converters, such as LP01 mode to LP02 mode and LP01 mode to LP21 mode, based on DHC-ARF.

Design of uncomplicated triangular core PCF for enhanced non-linearity applications

An innovative design of Photonic Crystal Fibre (PCF) for enhanced non-linearity applications using simulation with the Finite Element Method (FEM) is presented. The PCF is a kind of fibre optic waveguide that has air-holes along the entire length of the optical fibre, which exploits its exclusive features of being continuously single-moded and having a modifiable spot-size and dispersion properties for various linear and non-linear applications. This proposed triangular core PCF is made of silica material with a refractive index of 1.445 and features three large air-holes placed 120° apart in the core, each with a refractive index of 1.00. The air-holes have a pitch length of 6.03 μm and a radius of 2.86 μm, and the wavelength of operation is 1.55 μm. The proposed PCF design has a large diameter to pitch ratio (d/Λ) of up to 0.95, resulting in a reduced spot-size of just above 1.00 μm2. This indicates that the proposed triangular core PCF design could be used to enhance non-linearity applications. This study introduces a novel structure that simplifies construction by employing three strategically positioned large air-holes in the cladding, thus achieving the necessary properties for guiding light through the core. This streamlined approach overcomes complexities associated with previous designs from the literature, hence, offering a practical solution for effective light guidance while minimising construction difficulties. This inventive proposed PCF design can be fabricated using the Stack and Draw process or the slurry casting method.

Atomic surface induced by novel green chemical mechanical polishing for aspheric thin-walled crucibles with large diameters

Aspheric thin-walled crucibles with large diameters are widely used for photovoltaics and semiconductor industries, while they have hard-brittle and aspheric characteristics. Nevertheless, these crucibles strictly require atomic surfaces and high material removal rate (MRR). This is a challenge for chemical mechanical polishing (CMP). To break this challenge, a novel green CMP was developed for fused silica, containing ceria, lanthana, hydrogen peroxide, diethylene triaminepentaacetic acid pentasodium, carboxymethyl cellulose sodium and guanidine carbonate. After CMP, surface roughness Ra of 0.115 is obtained at a scanning area of 5 × 5 μm2 measured by atomic force microscopy, and MRR is 563 nm/min. In such an atomic surface, the MRR is the highest compared with those published previously. Transmission electron microscopy confirms that the thickness of damaged layer after CMP is only 2.63 nm. A novel approach of robot floating polishing is proposed for aspheric crucibles with a diameter of 810 mm and a height of 580 mm. Using the developed CMP, surface roughness Sa of 0.178 nm on inner surface of an aspheric thin-walled crucible is achieved under a measurement area of 50 × 50 μm2. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance reveal that the content of Ce3+ increased from 28.54 to 43.76 %. Through Raman, XPS and Fourier transform infrared spectroscopy, CMP mechanisms are elucidated. Densified damaged layer on the surface of fused silica was induced by the transformation of surface structure from six-membered to four- or three-membered network. Ce-OH and Si-OH were formed between fused silica and ceria abrasives, forming Ce-O-Si by condensation reaction of dehydration. The developed green CMP and approach provide new pathway to polish and manufacture atomic surfaces for aspheric thin-walled crucibles with large diameters.

Erosion characteristics of water droplet machining

Water Droplet Machining (WDM) is a new manufacturing process, which uses a series of high-velocity, pure-water droplets to impact and erode solid workpieces, for the purpose of through-cutting, milling and surface profiling. The process is conducted within a vacuum environment to suppress aerodynamic drag and atomization of the waterjet and droplet train. This preserves droplet momentum and allows for a more efficient transfer of energy between the water and workpiece, than in standard atmospheric pressure. As a new manufacturing technique, parameter-specific details and characteristics of this process are absent from the scientific literature. Therefore, this study aims to elucidate the capabilities of WDM, and uncover its erosion characteristics. Experiments are performed using a custom-fabricated machine, where a range of waterjet-types (and droplet trains) are produced. The experiments are performed on two industrial-relevant metals: stainless steel SS 316 L and aluminum AA 6022-T4. The target shape is a partial-cut through the material, i.e., a trench. A parametric study investigates the effects of stand-off distance, orifice diameter, and feed-rate on the trench shape, material-removal-rate, and reveals the conditions which render WDM an effective machining process. It was found that, for orifice diameters of 100 μm, an effective stand-off distance is between 457 and 686 mm; below that, no material removal is observed. In this configuration, accurate through-cuts are produced and can be used for manufacturing purposes. For large orifice diameters, e.g., 250 μm, an atomized spray is produced, which features a comparatively large material removal rate, and can be used for surface profiling and milling.

Study on stress distribution law of surrounding rock of roadway under the goaf and mechanism of pressure relief and impact reduction

To safely extract residual coal from a mine affected by rock bursts, the concept of “roadways under goafs” has been proposed as an effective layout. The pressure relief and shock reduction mechanism of roadways under goafs is elucidated through theoretical analysis, numerical simulation, and engineering verification. The stress model for goafs is established based on elastoplastic mechanics, followed by the construction of a force model for coal beneath the goafs. The stress composition of roof, floor and two sides of roadway under a goaf are analyzed. Using the FLAC-PFC coupling simulation method, the excavation process from top coal mining to bottom coal mining roadways of a No. 17 coal mine in Heilongjiang Province was simulated. The simulation results validate the spatiotemporal evolution of the stress and displacement in the surrounding rock mass of the roadway situated beneath goafs and determine the precise location of the roadway and length of its bottom coal face. A large diameter borehole of the roadway and presplitting blasting of the coal face roof are used to solve the local high stress danger area. Moreover, the roadway support mode of the “steel shed + spray arch support + monomer + π steel beam” is proposed. Finally, through the data of the field micro-seismic and stress monitoring system, the effectiveness of the pressure relief and shock reduction of roadways under goafs, the high efficiency of local danger relief of the roadways and working faces, and the practicability of the “steel shed + spray arch support + monomer + π steel beam” support of the roadways broken by surrounding rock are verified. A good basis for choosing a reasonable location for roadways and surrounding rock control methods for residual bottom coal mining and rock burst mining can be found in the research results.