Anisotropy Dependence of Material Deformation Mechanisms in Nanoscratching Monocrystalline BaF2: Experiments and Atomic Simulations.

Monocrystalline barium fluoride (BaF2), known for its exceptional optical properties in the infrared spectrum, exhibits anisotropy that influences surface quality and material removal efficiency during ultraprecision machining. This research explores the impact of anisotropy on the deformation and removal mechanisms of monocrystalline BaF2 by integrating nanoscratch tests with molecular dynamics (MD) simulations. Nanoscratch tests conducted on variously oriented monocrystalline BaF2 surfaces using a ramp loading mode facilitated the identification of surface cracks and a systematic description of material removal behaviors. This study elucidates the effect of crystal orientation on the ductile-brittle transition (DBT) of monocrystalline BaF2, further developing a critical depth prediction model for DBT on the (111) crystal plane to reveal the underlying anisotropy mechanisms. Moreover, nanofriction and wear behaviors in monocrystalline BaF2 are found to be predominantly influenced by scratch direction, crystal surface, and applied load, with the (110) and (100) planes showing pronounced frictional and wear anisotropy. A coefficient of friction model, accounting for the material's elastic recovery, establishes the intrinsic relationship between anisotropic friction and wear behaviors, the size effect, and scratch direction. Lastly, MD modeling of nanoscratched monocrystalline BaF2 reveals the diversity of dislocations and strain distributions along the (111) [-110] and [-1-12] crystal directions, offering atomic scale insights into the origins of BaF2 anisotropy. Thus, this study provides a theoretical foundation for the efficient processing of fluorine-based infrared optic materials exhibiting anisotropy.

Autoencoder assisted subcarrier optimization for nonlinear frequency division multiplexing.

Nonlinear frequency division multiplexing (NFDM) is a novel optical communication technique that can achieve nonlinear free transmission. However, current design of NFDM is analogous to orthogonal frequency division multiplexing (OFDM), where sinc function is utilized as subcarriers, which may not be optimal for nonlinear spectrums. In this paper, we propose an auto-encoder (AE) assisted subcarrier optimization scheme for dual-polarized (DP) NFDM systems. Numerical verifications show that our scheme can improve the Q-factor by 1.54 dB and 0.62 dB compared to sinc subcarrier and linear minimum mean square error (LMMSE) equalization, respectively, in a 960 km transmission scenario. We also analyze the characteristics of the optimized subcarriers and discuss how they enhance the performance. Furthermore, we demonstrate the robustness of the optimized subcarriers to different modulation formats, transmission distances and bandwidth. Our work provides a new idea in subcarrier design for NFDM.

Anisotropic Deformation Behavior and Indentation Size Effect of Monocrystalline BaF2 Using Nanoindentation.

In this study, our objective is to investigate the anisotropic deformation behavior and the indentation size effect (ISE) of monocrystalline barium fluoride (BaF2) using nanoindentation experiments with a diamond Berkovich indenter. BaF2 is known for its anisotropy, which results in significant variations in its mechanical properties. This anisotropy poses challenges in achieving high processing quality in ultra-precision machining. Through our experiments, we observed numerous pop-in events in the load-displacement curves, indicating the occurrence of plastic deformation in BaF2 crystals, specifically in the (100), (110), and (111) orientations; these pop-in events were observed as the indentation depth increased to 56.9 nm, 58.2 nm, and 57.8 nm, respectively. The hardness-displacement and elastic modulus-displacement curves were obtained from the tests exhibiting the ISE. The nanoindentation hardness of BaF2 is found to be highly dependent on its crystallographic orientation. Similarly, for BaF2 in the (100) orientation, the range is from 2.43 ± 0.74 and 1.24 ± 0.12 GPa. For BaF2 in the (110) orientation, the values range from 2.15 ± 0.66 to 1.18 ± 0.15 GPa. For BaF2 in the (111) orientation, the values range from 2.12 ± 0.53 GPa to 1.19 ± 0.12 GPa. These results highlight the significant influence of crystallographic orientation on the mechanical properties of BaF2. To better understand the ISE, we employed several models including Meyer's law, the Nix-Gao model, the proportional specimen resistance (PSR) model, and the modified PSR (mPSR) model, and compared them with our experimental results. Among these models, the mPSR model demonstrated the best level of correlation (R2>0.9999) with the experimental measurements, providing a reliable description of the ISE observed in BaF2. Our reports provide valuable insights into the anisotropic mechanical characteristics of BaF2 materials and serve as a theoretical guide for the ultra-precision machining of BaF2.

Improvement for a full-spectrum modulated nonlinear frequency division multiplexing transmission system.

Nonlinear frequency division multiplexing (NFDM), as a possible technique to overcome the limit imposed by Kerr nonlinearity in conventional coherent optical communication systems, has attracted widespread attention in the communication community in recent years. In order to fully utilize the available degrees of freedom in the nonlinear spectrum, this paper focuses on the full-spectrum (FS) modulated NFDM system. First, we maximize the data rate of discrete spectrum (DS) by optimizing the distribution of eigenvalues in DS part of FS. Then through introducing the probabilistic shaping (PS) into the FS system, and combined with linear minimum mean square (LMMSE) estimators, a 1120 km transmission with BER below the hard decision forward error correction (HD-FEC) threshold at 112 Gbps is achieved, where 128 subcarriers with PS-64QAM are used in the continuous spectrum (CS) and 13 eigenvalues with 64QAM are adopted in the discrete spectrum (DS). The achievable data rate is about 12% higher than that of pure CS modulation. Our work achieves the current FS NFDM system with the largest number of multiplexed eigenvalues, and provides a way to improve the performance of FS systems.

Optimisation of Lapping Process Parameters for Single-Crystal 4H-SiC Using Orthogonal Experiments and Grey Relational Analysis.

Lapping is one of the standard essential methods to realise the global planarization of SiC and other semiconductor substrates. It is necessary to deeply study the mechanism to obtain SiC lapping process parameters with a strong comprehensive lapping performance (i.e., high material removal rate (MRRm), small surface roughness (Ra), and low total thickness variation (TTV)). The effects of the lapping process parameters and their interactions on lapping performance for SiC were investigated using orthogonal experiments; the effects on the MRRm, Ra, TTV, and optimal parameters under the conditions of a single evaluation index were investigated using intuitive analysis (range analysis, variance analysis, and effect curve analysis). The entropy value method and grey relational analysis were used to transform the multi-evaluation-index optimisation into a single-index optimisation about the grey relational grade (GRG) and to comprehensively evaluate the lapping performance of each process parameter. The results showed that the lapping plate types, abrasive size, and their interaction effect had the most significant effects on MRRm and Ra, with a contribution of over 85%. The interaction between the lapping plate types and abrasive size was also found to have the most significant effect on TTV, with a contribution of up to 51.07%. As the lapping plate's hardness and abrasive size increased, the MRRm and Ra also gradually increased. As the lapping normal-pressure increased, MRRm increased, Ra gradually decreased, and TTV first decreased and then increased. MRRm, Ra, and TTV first increased and then decreased with increasing abrasive concentration. Compared to the optimisation results obtained by intuitive analysis, the process parameter optimised by the grey relational analysis resulted in a smooth surface with an MRRm of 90.2 µm/h, an Ra of 0.769 nm, and a TTV of 3 µm, with a significant improvement in the comprehensive lapping performance. This study reveals that a combination of orthogonal experiments and grey relational analysis can provide new ideas for optimising the process parameters of SiC.

Probabilistic shaping and neural network-based optimization for a nonlinear frequency division multiplexing system.

A joint scheme introducing probabilistic shaping (PS) at the transmitter and utilizing a neural network (NN) equalizer at the receiver is proposed to improve the performance of the b-modulated nonlinear frequency division multiplexing (NFDM) system. Through a numerical simulation, we demonstrate that PS plays a leading role for low launch power case, which improves the performance of the system effectively, while the NN equalizer's superiority appears in a high launch power region, whose main role is to weaken the correlation among subcarriers for improving system performance. The proposed scheme would enlighten the optimum modulation and detection schemes of the NFDM system.

Scratch Behaviour of Bulk Silicon Nitride Ceramics.

Si3N4 ceramic is generally recognized as being difficult to machine due to its hardness and brittleness. It is necessary to control the normal load applied and the machined depth of the abrasive particles in order to eliminate surface/subsurface damage and defects during the grinding or polishing. In this study, scratch experiments were conducted on the polished surface of Si3N4 specimens to investigate the brittle-ductile transformation and the evolution of material removal mechanisms. In addition, the cracking behaviour of Si3N4 ceramic was characterized by indentation tests. The Vickers indentation produced cracks that exhibited good developmental integrity and geometric symmetry. The results indicate that the scratch track can be divided into three stages: the ductile regime, the brittle-ductile coexisting stage, and the brittle fracture regime. The critical loads and the corresponding penetration depths of cracking occurrence in Si3N4 were recorded. The material removal of Si3N4 ceramic was primary attributed to ductile regime removal when the load was less than 9.8 N. Microcrack initiation on the subsurface was observed when the penetration depth of the scratch tip reached 8 µm or the depth of the indentation tip reached 3.2 µm. Microcracks expanded rapidly as the load was further increased, resulting in a brittle fracture of the Si3N4 ceramic.

Effective prevention and management of COVID-19 in outpatient hemodialysis patients.

The authors introduce a mobile phone app that may effectively prevent and manage coronavirus disease 2019 (COVID-19) in outpatient hemodialysis patients in Sichuan Province, China.

Prevalence of Kaschin-Beck disease among Tibetan children in Aba Tibetan and Qiang Autonomous Prefecture: a 3-year epidemiological survey.

BACKGROUND: Kaschin-Beck disease (KBD), a special type of osteoarthritis, is a disabling degenerative disease and it can cause severe dysarthrosis of joints. This study was undertaken to investigate the prevalence of KBD among Tibetan children in the Aba Tibetan and Qiang Autonomous Prefecture in Sichuan Province and to provide evidence for KBD control in the western regions of China. METHODS: Eleven counties were selected as the monitoring regions and all Tibetan children aged 6-13 years were selected as the study subjects. A questionnaire survey and clinical and radiological examinations (right hand and wrist) were performed. KBD was diagnosed according to the Chinese Radiological Criteria of Kaschin-Beck Disease Diagnosis (GB16003-1995). RESULTS: X-ray analysis showed that all counties belonged to controlled endemic areas, and 4 of them were confirmed as active endemic areas for KBD. The overall detection rate of KBD in the Aba Tibetan and Qiang Autonomous Prefecture was 2.09% in 2007, 2.66% in 2008, and 1.20% in 2009. The majority of pediatric patients were found in Jinchuan and Markang counties. CONCLUSIONS: Although the prevalence of KBD showed a decreasing trend in the Aba Tibetan and Qiang Autonomous Prefecture, some new pediatric cases are still emerging. Therefore, comprehensive measures should be taken to prevent the occurrence of the disease in children, and an effective preventive program should be set up in the prefecture.

Genetic variants in the HLA-DRB1 gene are associated with Kashin-Beck disease in the Tibetan population.

OBJECTIVE: To investigate the association between variants in the HLA-DRB1 gene and Kashin-Beck disease (KBD), as well as associations of selenium and iodine deficiencies with KBD in a Tibetan population. METHODS: Fourteen single-nucleotide polymorphisms (SNPs) were genotyped around the HLA-DRB1 gene, and HLA-DRB1 allele genotyping was performed in a discovery cohort, composed of 605 patients with KBD and 393 control subjects, and/or a replication cohort, composed of 290 patients with KBD and 295 controls. Plasma concentrations of selenium and iodine were measured and compared by t-test in 299 patients with KBD and 280 controls from the same villages. RESULTS: Four SNPs (rs6457617, rs6457620, rs9275295, and rs7745040) in the HLA-DRB1 gene locus were significantly associated with KBD in both the discovery cohort and replication cohort (combined cohort odds ratios [ORs] 1.307-1.402, P = 0.0039-0.0006). The protective haplotype GTCC and the risk haplotype ACGT, each generated by the 4 SNPs, showed a significant association with KBD (for GTCC, OR 0.77, P = 0.0031; for ACGT, OR 1.40, P = 0.0014). HLA-DRB1 allele genotyping revealed that the frequencies of HLA-DRB1*08 and *11 were significantly different between patients with KBD and controls (for HLA-DRB1*08, OR 0.731, P = 0.00564; for HLA-DRB1*11, OR 0.489, P = 0.000395). Moreover, plasma concentrations of selenium and iodine were significantly different between patients with KBD and controls from the same villages (P = 0.0013 and P = 1.84 × 10(-12) , respectively). CONCLUSION: These findings, obtained in plasma samples from Tibetan patients with KBD and healthy control subjects from the same regions, confirm the role of selenium and iodine deficiencies in the development of KBD. Moreover, genetic variants in the HLA-DRB1 gene significantly increase the susceptibility to KBD in this population.

The effect of Kashin-Beck disease-affected feed and T-2 toxin on the bone development of Wistar rats.

OBJECTIVE: To investigate the effect of Kashin-Beck disease (KBD)-affected feed and T-2 toxin on the bone development of Wistar rats. METHODS: Seventy-eight ablactation Wistal rats (50% male and 50% female) weighing approximately 65 g were obtained from Sichuan Medical Center (Chengdu, China), and were randomly assigned to three groups (Groups A, B and C). Group A had 24 rats and were fed with commercial rat feed (control); Group B had 30 rats and were fed with commercial rat feed and T2 toxin by intragastric administration; and Group C had 24 rats and were fed with the KBD-affected feed. The histological sections were stained with hematoxylin and eosin (H&E) and Masson dye. RESULTS: Weight gain was fastest Group A rats and Group C rats had the lowest weight gain (P < 0.05). There were no epiphyseal plate chondrocyte necroses in the control group at the first, second, and fourth weeks. In the T-2 toxin group, two rats had chondrocyte-focus necroses at the labrocyte cell zone at the second week. At the fourth week, six rats had chondrocyte-focus or lamellar necroses at the labrocyte cell zone. Three rats had focus necrosis at the proliferation cell zone, and there were three rats with penetration necrosis. In the KBD-affected group, one rat had chondrocyte-focus necrosis at the labrocyte cell zone at the second week and seven rats had chondrocyte-focus necrosis at the labrocyte cell zone at the fourth week. And at the same time, two rats had focus necrosis at the proliferation cell zone, three rats had lamellar necrosis at the labrocyte cell zone, four had focus necrosis at the labrocyte cell zone, and two rats had penetration necrosis. The epiphyseal plate Masson dye of the control group showed deep blue collogen coloration and in the KBD-affected group and T-2 toxin group, collogen showed a pale blue color, the drum dyeing was uneven, and the collogen was showed an absence of color in the region of the necrosis. CONCLUSIONS: With KBD-affected feed or T-2 toxin intervention, rats had focus necrosis and lamellar necrosis at the epiphyseal plate. KBD-affected feed rats had less weight gain than T-2 toxin intervention rats, which means there were other etiological factors in KBD-affected feed.

[Surveillance on Keshan disease from 1990 to 2008 in Sichuan province].

OBJECTIVE: To study the epidemiological characteristics of Keshan disease (KD) and its trend so as to provide evidences for further research, prevention and treatment of the disease in Sichuan province. METHODS: Based on KD related data from 1990 to 2008, descriptive method was used to analyze the epidemiological characteristics of KD. RESULTS: 87 KD cases were identified during the 19 years. All cases were children from the countryside, with majority of them were Yi nationality. Age of the patients ranged from 5 months to 18 years, with majority at 2 - 6 year-olds. The annual incidence rates were from 0/100 000 to 1.73/100 000 with 1999 the highest (1.73/100 000). A total number of 310 preclinical or chronic KD cases were identified and the total detection rates were between 0.28% and 2.8%, with 1992 the highest. As for levels of blood selenium during the 19 years: 1995 appeared the lowest (0.1345 microg/g), followed by 1990 - 2000 (0.1558 microg/g) but all of them fell in to the level in the KD epidemic areas. CONCLUSION: There were 5 stages in the development trend of KD disease in Sichuan province, with 2 ascending and 3 descending. The differences between any of the two stages were statistically significant. The 3 descending stages all appeared right after the selenium supplement intervention was taken. Our data showed that the program of selenium supplement was closely related to the incidence of KD, suggesting that a long term mechanism of Selenium supplement in the epidemic areas should be taking into account.