Search

Corner is one of the typical characteristics of aerospace monolithic components. In order to achieve a stable processing environment and reduce the mutation of milling force in the process of machining, the manufacturer has been searching a method to control the milling force of corner machining. Based on the cutting contact relationship and the instantaneous chip thickness, the milling force prediction model of corner machining is established. By analyzing different types of corner contact relationship, the influence of cutting contact angle and cutting arc length on milling force is established. The corner feed rate iterative calculation method is used to improve the corner milling force mutation. The corner milling experiment proves that the proposed method can not only effectively control the corner milling force, but also improve the surface quality of the bottom surface of the workpiece. The proposed method is suitable for automatic programming of multi-corner pocket machining and provides theoretical support for stable machining of frame part.

As infrastructure construction advances toward the cold and highland environment, concrete preparation technology and service performance in the cold climate is receiving much attention. The freezing of pore water inside concrete leads to significant changes in its mechanical properties at negative temperatures. Therefore, to ensure the safety of civil engineering structures in cold regions, it is necessary to fully understand the change law and enhancement mechanism of the mechanical properties of concrete and be able to predict mechanical properties at a negative temperature. Since the 1970s, scholars have studied concrete’s negative temperature mechanical properties in different water-content states. This paper presents a comprehensive review of the changes in mechanical properties of concrete at low and ultra-low temperatures and further elucidates the evolution of its compressive strength, tensile strength, flexural strength, elastic modulus, and stress-strain relationship at low temperatures. It was found that the main factors affecting the mechanical properties of concrete at low temperatures were temperature and moisture content. The strength of concrete increases significantly with the decrease in temperature and the increase in moisture content. To better understand and predict the mechanical properties of concrete at low temperatures, the best model was suggested by analyzing the prediction models of different researchers and considering the dispersion of the data. Further, based on the G. Wiedemann pore model, the changes in the internal structure of concrete at low temperatures are described in detail, and the mechanism of its mechanical property enhancement is analyzed.

Owing to poor hole-injection efficiency, conventional AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) generally suffer from a seriously inhomogeneous carrier distribution in the quantum well region. This leads to uneven radiative recombination rates, seriously affecting the luminous efficiency. In this paper, however, we propose an asymmetric quantum well (AQW) near the interface between the last quantum barrier and the electron blocking layer to fully utilize the inhomogeneous distribution characteristics. The optoelectronic performances of conventional and a proposed DUV-LED with an AQW have been numerically simulated and analyzed. The results reveal that electrons and holes tend to gather and recombine in the AQW region. This significantly enhances the internal quantum efficiency and the light output power with an improvement of about 120%, although it increases the peak emission wavelength red-shift. The peak emission wavelength of the AQW can be adjusted to the wavelength of the original structure while keeping a high optical efficiency by simply increasing the Al composition.

Deformation is an unavoidable phenomenon in a thin-walled milling operation, which causes the radial cutting depth to deviate from the initial position and change the tool-workpiece meshing boundary. Milling force is an important factor in the deformation; thus, the phenomenon of machining deformation mechanism is revealed and a machining error prediction model based on the force-deformation coupling relationship is developed in this paper. Discrete micro-cutting disks of the thin-walled parts take into account the deformations and milling cutting force of different contact relationships in the cutting area. The tool-workpiece contact relationship (single-flute cutting and double-flute cutting) is determined by different cutting parameters and the deflection of thin-walled parts is introduced. A detail iterative strategy is developed to calculate the milling force after deformation and the tool-workpiece meshing boundary. By modifying the instantaneous chip thickness of each micro-cutting disk, a new force-deformation coupling relationship and a time-based deformation matrix of different contact relationships are obtained. The machining error is calculated by considering the part deformation and the surface generation mechanism. After finishing systematic experiments, a comprehensive comparison between the model in mechanical prediction and experiments proves that the model captures the material removal mechanism that produces machining error. The results show that the proposed method can effectively predict the machining error.

In the milling process of titanium alloy thin-walled parts, because of its low stiffness, processing deformation easily occurs, which results in in low-dimensional accuracy of machined surface and affecting the workpiece performance. Cutting force is the main factor that causes cutting deformation. Cutting deformation also affects cutting force. There is a coupling relationship between them. To solve the above problems, a method is proposed to predict the surface error by calculating the milling force by varying the chip thickness and by coupling the force with the elastic deformation of the workpiece. Firstly, the analytical model of bending elasticity deformation of thin-walled parts is established. Then, the micro-unit entrance angle and instantaneous chip thickness are calculated by the contact relationship of workpiece deformation and the chip boundary decision conditions. The cutting force and workpiece deformation at random rotating angle are obtained by iterative calculation method. Finally, the surface error is predicted by calculating the deformation matrix and the principle of surface generation mechanism. The simulation results are in good agreement with the experimental results, which verifies the accuracy of the proposed method. The results provide theoretical support for milling process optimization and profile accuracy control of titanium alloy thin-walled parts.

Our aims were to evaluate protein tyrosine phosphatase nonreceptor type 22 (PTPN22) gene polymorphisms in ulcerative colitis (UC) and explore PTPN22 mRNA levels in colonic biopsies of UC patients in central China.A total of 165 Chinese UC patients and 300 healthy controls were enrolled in this study. PTPN22 -1123G/C, +1858C/T, and +788G/A polymorphisms were genotyped by PCR-restriction fragment length polymorphism method. PTPN22 mRNA expressions in colonic biopsies and serum C-reactive protein (CRP) levels were determined by quantitative PCR and immunonephelometry, respectively.The frequency of C carrier was higher in UC patients than in healthy controls (66.7 vs. 53.3%, P = 0.005, odds ratios = 1.75, 95% CI 1.18-2.60) and associated with extensive colitis (P = 0.029). PTPN22 mRNA levels were elevated in UC patients than in healthy controls (P 0.001). Among UC patients, PTPN22 mRNA expression levels were higher in biopsies of inflamed colonic tissue compared with noninflamed tissue (P 0.001) and were correlated with CRP levels (r = 0.578, P 0.001). PTPN22 mRNA expression levels were elevated in extensive colitis compared to proctitis (P = 0.008) and to left-sided colitis (P = 0.029) and were higher in moderate and severe disease than in mild disease (P = 0.005).Our study showed the potential association between PTPN22 -1123G/C polymorphism and UC in central China. PTPN22 mRNA levels were highly expressed in UC, especially in active disease, and were correlated with CRP levels, disease location, and disease severity in UC patients.

The hydrophobic ionic liquid [BMIM]PF6 (1-butyl-3-methylimidazolium hexafluorophosphate) can interact with sodium dodecyl sulfate (SDS) micelles in aqueous solution and modify their physicochemical properties to produce a unique separation efficiency in micellar electrokinetic chromatography (MEKC). An MEKC method was developed using [BMIM]PF6 as a modifier for separating eight fluoroquinolone compounds (ciprofloxacin, enrofloxacin, gatifloxacin, ofloxacin, norfloxacin, enoxacin, pazufloxacin, and tosufloxacin). The effects of several parameters on the separation selectivity, e.g., pH, concentration of background electrolyte, concentration ratio and amount of [BMIM]PF6 and SDS, were investigated. Under the optimal conditions of 10 mmol L−1 sodium borate, pH 7.1, 1.7% (w/w) SDS, 1.5% (w/w) [BMIM]PF6 with 18 kV as running voltage, the eight investigated quinolone compounds were baseline separated within 15 min. The selectivity of the developed method differed from that of the simple SDS micelles system containing no ionic liquid. The results suggest that hydrophobic ionic liquids should be promising modifiers in capillary electrophoresis, especially in MEKC analysis.

A detailed study is presented on magnetic, electrical and optical properties of Ga1−xMnxN: Si film grown by metal organic chemical vapor deposition (MOCVD) with high-purity SiH4 as the Si dopant source. The room-temperature field dependence magnetization and zero-field-cooled (ZFC)/field-cooled (FC) measurements indicate that the film remains room-temperature ferromagnetism and it declines slightly after Si co-doping. However, room-temperature Hall measurements indicate that the electrical property of the film improves distinctly compared with Ga1−xMnxN. Cathode luminescence (CL) measurements show an obvious enhancement in luminous property and different peak strength changes at three different positions. Therefore, we demonstrate that Fermi level and the electron structure of Mn atoms will change with variation of the impurities co-doped and the intrinsic defects and this may be related with room-temperature ferromagnetism and the other corresponding properties of the film.

Room-temperature ferromagnetism with a Curie temperature higher than 380 K was studied in GaN: Mn thin films grown by metal-organic chemical vapor deposition. By etching artificial microstructures on the GaN: Mn layer, strong magnetic responses were observed in the magnetic force microscopy (MFM) measurement, which revealed that the films were independent of dopant particles and clusters. Numerical simulation on the data of atomic force microscope (AFM) and MFM measurements covering the whole microstructure validated the formation of long range magnetic order. This result excluded a variety of controversial origins of room-temperature ferromagnetism in the GaN: Mn and gave a strong evidence of our GaN: Mn as the intrinsic diluted magnetic semiconductor (DMS). The forwarded method for accurate characterization of long range magnetic order could be applied to a wide range of DMS and diluted magnetic oxide (DMO) systems.

Reduced cytotoxic T-lymphocyte antigen 4 (CTLA4) expression has been proposed as a risk for autoimmunity. CTLA4 polymorphisms have been associated with several autoimmune diseases, including ulcerative colitis (UC). In this study, we performed genotyping for CTLA4 -1661A/G, -1722T/C and 3' untranslated region (AT)n repeat polymorphisms in 300 Chinese UC patients and in 700 healthy controls, and evaluated the effects of polymorphisms on full-length (flCTLA4) and soluble CTLA4 (sCTLA4) expression in UC patients. The frequency of the -1661G allele was higher in UC patients than in healthy controls (16.5 vs 11.4%, P=0.003, odds ratio (OR)=1.53, 95% confidence interval (95% CI): 1.17-2.01). The prevalence of (AT)n repeats of the CTLA4 gene carrying long alleles (≥116 bp) was more common in UC patients than in healthy controls (22.0 vs 6.3%, P0.001, OR=4.21, 95% CI: 2.79-6.33), and was associated with extensive colitis (P=0.008). Among UC patients, long-allele carriers expressed lower levels of flCTLA4 and sCTLA4 mRNA and sCTLA4 protein than did short-allele carriers (P0.001, P0.001, P0.001, respectively). CTLA4 gene -1661A/G and long 3' untranslated region (AT)n repeat polymorphisms are associated with UC in Central China. This is likely from decreased expressions of sCTLA4 mRNA and sCTLA4 protein. Our study suggests that CTLA4 has an important role in susceptibility for UC in Central China.