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This study utilized ion implantation to modify the material properties of silicon carbide (SiC) to mitigate subsurface damage during SiC machining. The paper analyzed the mechanism of hydrogen ion implantation on the machining performance of SiC at the atomic scale. A molecular dynamics model of nanoscale cutting of an ion-implanted SiC workpiece using a non-rigid regular tetrakaidecahedral diamond abrasive grain was established. The study investigated the effects of ion implantation on crystal structure phase transformation, dislocation nucleation, and defect structure evolution. Results showed ion implantation modification decreased the extension depth of amorphous structures in the subsurface layer, thereby enhancing the surface and subsurface integrity of the SiC workpiece. Additionally, dislocation extension length and volume within the lattice structure were lower in the ion-implanted workpiece compared to non-implanted ones. Phase transformation, compressive pressure, and cutting stress of the lattice in the shear region per unit volume were lower in the ion-implanted workpiece than the non-implanted one. Taking the diamond abrasive grain as the research subject, the mechanism of grain wear under ion implantation was explored. Grain expansion, compression, and atomic volumetric strain wear rate were higher in the non-implanted workpiece versus implanted ones. Under shear extrusion of the SiC workpiece, dangling bonds of atoms in the diamond grain were unstable, resulting in graphitization of the diamond structure at elevated temperatures. This study established a solid theoretical and practical foundation for realizing non-destructive machining at the atomic scale, encompassing both theoretical principles and practical applications. [ABSTRACT FROM AUTHOR]

In this paper, a new method is developed for tool path planning on triangular mesh surfaces with consideration of the scallop height restriction and the path smoothness. This method first maps the triangular mesh surface into a unit disk region by using a harmonic map algorithm, and then the shortest boundary path graph (SBPG) is constructed on the unit disk region to describe the shortest geodesic distance from each mesh vertex to the surface boundary. The tool path is then obtained by inversely mapping the contours of SBPG from the harmonic mapped region to the physical space of mesh surface. During this process, a subdivision method is used to boost the computing efficiency and a smoothing treatment is conducted on the SBPG to improve the path smoothness. The tool path planning is performed starting from the surface boundary in an iteration process. Taking the level difference of SBPG contours as the initial path interval and being supplemented by a correction process, the maximal step distance between any two paths, which meets the requirement of scallop height restriction, can be determined efficiently. Typical simulation cases and experiments are carried out to illustrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Tool path planning is critical to fully realise the producing capabilities of multi-axis machine tools and improve the precision and efficiency in multi-axis machining. Up to now, more than 400 articles have been published for tool path planning of multi-axis machine tools. Among them, most of the articles mainly focus on the topology of tool path while few studies are conducted for planning of tool orientation. Moreover, the factors that affect the planning of tool orientation are derived from multiple aspects, such as interference, collision and cutting strip width, which poses great challenges on tool orientation planning. To generate a time-optimal tool path with high machining precision, there is an urgent need to ascertain the influences of tool orientation arrangement on the multi-axis machining process. Therefore, in this work, a literature review on tool orientation planning of multi-axis machine tools is implemented. The main factors that influence the planning of tool orientations are systematically summarised, and the advantages and disadvantages of the corresponding methods related to these factors are discussed. Some research issues and challenges encountered in the tool orientation planning are identified. Furthermore, the methodologies that have potential to address the research issues in the future are prospected. [ABSTRACT FROM AUTHOR]

Modular input-series–output-parallel (ISOP) converters are very suitable for high-voltage and high-power applications. In order to ensure the normal operation of ISOP converters, it is necessary to realize the input-voltage and output-current equalization of each submodule. However, there are few studies on the input-voltage and output-current equalization performance of the ISOP system. In this paper, the input-voltage and output-current equalization characteristics of a Boost + LLC modular ISOP converter are studied based on the small-signal model. In this paper, the small-signal model of an ISOP system is first established, and then the input-voltage and output-current equalization performance of the ISOP system under the condition of inconsistent submodule parameters are analyzed. Finally, simulations and experiments are reported to verify the results. The experimental results show that the ISOP system composed of a Boost + LLC cascaded module has excellent voltage and current self-equalization performance. [ABSTRACT FROM AUTHOR]

Wide-bandgap ZnGa2O4 (ZGO) semiconductor nanoparticles with oxygen vacancies were prepared by a hydrothermal method via microwave heating at temperatures less than 120 °C using a domestic microwave with an irradiation time as short as 150 s. The effect of pH of the precursor solution on the structural and optical properties of the ZnGa2O4 nanoparticles was investigated. The solution pH hardly affected the ZnGa2O4 particle size; the sizes remained almost unchanged in the range from 4.98 ± 0.09 to 6.32 ± 0.07 nm as pH was varied between 5.2 and 7.0. However, with decreasing solution pH, the number of oxygen vacancies increased owing to the generation of zinc deficiencies in the ZnGa2O4 nanoparticles. Consequently, the bandgap increased with decreasing pH, reaching a maximum of 4.78 eV at pH 5.2, when the ZnO/Ga2O3 molar ratio in the nanoparticles was the lowest (= 0.18). Moreover, the photoluminescence intensity also increased with decreasing pH, without any spectral shift. The photoluminescence was not dominated by the quantum size effect, but by the number of oxygen vacancies. The rapid and low-temperature microwave-based synthesis strategy of ZnGa2O4 nanophosphors developed in this study is expected to provide an energy-saving method for producing nanoparticles with controlled optical properties, contributing to future optoelectronic device applications. [ABSTRACT FROM AUTHOR]

Optical interferometry plays an important role in the topographical surface measurement and characterization in precision/ultra-precision manufacturing. An appropriate surface reconstruction algorithm is essential in obtaining accurate topography information from the digitized interferograms. However, the performance of a surface reconstruction algorithm in interferometric measurements is influenced by environmental disturbances and system noise. This paper presents a comparative analysis of three algorithms commonly used for coherence envelope detection in vertical scanning interferometry, including the centroid method, fast Fourier transform (FFT), and Hilbert transform (HT). Numerical analysis and experimental studies were carried out to evaluate the performance of different envelope detection algorithms in terms of measurement accuracy, speed, and noise resistance. Step height standards were measured using a developed interferometer and the step profiles were reconstructed by different algorithms. The results show that the centroid method has a higher measurement speed than the FFT and HT methods, but it can only provide acceptable measurement accuracy at a low noise level. The FFT and HT methods outperform the centroid method in terms of noise immunity and measurement accuracy. Even if the FFT and HT methods provide similar measurement accuracy, the HT method has a superior measurement speed compared to the FFT method. [ABSTRACT FROM AUTHOR]

Biometric measurement of the anterior segment is of great importance for the ophthalmology, human eye modeling, contact lens fitting, intraocular lens design, etc. This paper serves as a comprehensive review on the historical development and basic principles of the technologies for measuring the geometric profiles of the anterior segment. Both the advantages and drawbacks of the current technologies are illustrated. For in vivo measurement of the anterior segment, there are two main challenges that need to be addressed to achieve high speed, fine resolution, and large range imaging. One is the motion artefacts caused by the inevitable and random human eye movement. The other is the serious multiple scattering effects in intraocular turbid media. The future research perspectives are also outlined in this paper. [ABSTRACT FROM AUTHOR]

The cascade converter system has been widely concerned along with the medium power operating conditions, and it is crucial to address the intricate interplay among individual modules to ensure stability of both the source and load subsystems. This paper analyzes the DC‐link voltage stability based on impedance matching and proposes a normalized sensitivity calculation method based on the control strategy, which prevents the complex products and matrix calculations of traditional methods. The three‐level boost (TLB) output impedance model is derived based on state‐space averaging for open‐loop and considering the double‐loop, and the full‐bridge LLC (FBLLC) input impedance model is derived based on the fundamental equivalent circuit. Then the effect of the double‐loop PI parameters on the output impedance of the TLB is analyzed in detail based on the normalized sensitivity and verified by the Bode plots. The experimental results of the 30 kW prototype indicate that the control parameters were varied by a factor of 10 compared to the theoretical control group. The most significant alteration was the modification of the kp_i, resulting in an 8.9% increase in the DC‐link voltage ripple, while the ki_v was modified, resulting in a 0.53% increase, indicating that the effects of the PI parameter are consistent with the normalized sensitivity results. [ABSTRACT FROM AUTHOR]

Objectives: The study aimed to compare the treatment cost, operation time, clinical effect, and complications between punctures done under magnetic resonance imaging (MRI) planning based on picture archiving and communication systems (PACS) and punctures done under immediate X-ray fluoroscopy guidance in the treatment of lumbar disc herniation by transforaminal lumbar epidural injection., Patients and Methods: In this prospective study conducted between October 2016 and June 2021, 128 patients were randomly divided into Groups A and B by the random number table method. In Group A (n=66; 36 males, 30 females; mean age: 64.5±2.4 years, range, 50 to 72 years), puncture was performed by planning with PACS-based MRI; in Group B (n=62; 34 males, 28 females; mean age: 65.3±2.6 years; range, 48 to 73 years), puncture was performed under immediate X-ray guidance. The cost of treatment, duration of procedure, clinical outcome, and complications were compared between the two groups., Results: The difference in treatment cost in Groups A and B was statistically significant (p<0.001), with 755.67±29.45 yuan and 1.158.08±43.92 yuan, respectively. The mean treatment time was statistically significant (p<0.001) between the groups, with 21.16±1.91 min in Group A and 37.26±2 min in Group B. However, there was no significant difference between Group A and Group B in terms of improvement in pain scores and Oswestry disability index (both p>0.05). There was also no significant difference between Group A and Group B in terms of complication rates (both p>0.05)., Conclusion: Compared to immediate X-ray guided puncture, the puncture method using PACS for MRI planning shortened the transforaminal lumbar epidural injection procedure time and reduced the treatment costs without exposing the physician or patient to additional radiation, while there was no significant difference in the short-term clinical outcome or complication rate.

Various micro-structure surface texturing methods have been used to produce optical functional surface in the grinding, such as the textured grinding wheel, wheel path control and off-spindle-axis grinding. However, those grinding technologies are inherently challenged to employ in large-scale surface grinding due to the extremely high requirement for wheel cutting profile dressing. In this study, a novel phase shift modulation based on wheel oscillation motion was proposed to generate the micro-structure array in ultra-precision grinding. The phase shift effect involved in the surface micro-structure generation is investigated, in which the role of the second phase shift on superimposed mode and micro-waviness forms is discussed. A theoretical model based on the tool superimposed oscillation is established to study the micro-structure texture generation mechanism by considering the second phase shift. The influence of modulation frequency in the case of phase shift and out of phase shift on the surface texture generation both for the striation pattern and micro-structure is compared to clarify the transition between the continuous grooves and the discrete micro-structure array. The study indicates that the phase shift modulation represents a novel paradigm for fabricating micro-structure array with considerable capability and high efficiency in ultra-precision grinding.