Cutting Force Transition Model Considering the Influence of Tool System by Using Standard Test Table.

The cutting force prediction model usually uses the classical oblique transformation method, which introduces the orthogonal cutting parameters into the oblique milling edge shape, and combines the geometric parameters of the tool to convert the orthogonal cutting force into the actual cutting force, thereby predicting the cutting force. However, this cutting force prediction method ignores the impact of tool vibration in actual machining, resulting in a large difference between the prediction model and the actual measurement. This paper proposes a cutting force conversion model considering the influence of the tool system. The proposed model fully considers the impact of tool vibration on the cutting force. On the basis of the orthogonal model, superimposing the additional cutting force generated by tool vibration makes the predicted value of the model closer to the actual cutting force. The results of milling experiments show that the conversion model can obtain higher prediction accuracy. Moreover, compared with the original conversion model, the accuracy of the proposed model is significantly improved.

Post-processing method for the removal of mixed ring artifacts in CT images.

Ring artifacts seriously deteriorate the quality of CT images. Intensity-dependence of detector responses will result in intensity-dependent ring artifacts and time-dependence of CT hardware systems will result in time-dependent ring artifacts. However, only the intensity-dependent ring artifacts are taken into consideration in most post-processing methods. Therefore, the purpose of this study is to propose a general post-processing method, which has a significant removal effect on the intensity-dependent ring artifacts and the time-dependent ring artifacts. First in the proposed method, transform raw CT images into polar coordinate images, and the ring artifacts will manifest as stripe artifacts. Secondly, obtain structure images by smoothing the polar coordinate images and acquire texture images containing some details and stripe artifacts by subtracting the structure images from the polar coordinate images. Third, extract the stripe artifacts from the texture images using mean extraction and texture classification, and obtain the extracted ring artifacts by transforming the extracted stripe artifacts from polar coordinates into Cartesian coordinates. Finally, obtain corrected CT images by subtracting the extracted ring artifacts from the raw CT images, and iterate the corrected CT images in above steps until the ring artifacts extracted in the last iteration are weak enough. Simulation and real data show that the proposed method can remove the intensity-dependent ring artifacts and the time-dependent ring artifacts effectively while preserving image details and spatial resolution. In particular, real data prove that the method is suitable for new CT systems such as the photon counting CT.

Scattering measurement and estimation in angular sequence for cone-beam CT based on projection structural tensor and modeling.

Based on the structural tensor of projection, this study aims to address and test a new improved algorithm applying to the distort projection data to generate a high qualified image by reducing the artifacts and noise from scattering in the cone-beam computed tomography (CBCT). Since the scattering information has a large relationship with the structure of the object, which is reflected by the projection, regional model knowledge for scattering is accomplished by finding the relationship between projection and scattering. As the tensor, the gradient of projection is first calculated in the process for estimating the direction and structural edge of the object. Then, the Determinant and Traces of the tensor map with different characteristics are computed to determine the different regions. By modeling and fitting the regions of scattering distribution, the knowledge of scattering parameters corresponding to a different region is obtained. Based on the similarity of scattering distribution in adjacent angles, the scatterings with angle sequence are completed by interpolating the prior knowledge obtained through the sparse sampling. By performing the studies on polychromatic X-ray to test the performance of the scattering estimation algorithm, the results show a significant improvement in the images that are reconstructed from the corrected projection. The root mean square error (RMSE) of the proposed method is reduced by 21.8% and 39.8%, respectively. Peak signal to noise ratio (PSNR), and universal quality index (UQI) also indicate better uniformity, where the PSNR is increased by 7.4% and 56.7%, UQI is increased by 70.8% and 262.3% for experimental #Wheel and #Cylinder, respectively.

A CBCT series slice image segmentation method.

BACKGROUND: Images of industrial cone-beam computed tomography (CBCT) contain noise and beam hardening artifacts, which induce difficulty and low precision in segmenting regions of interest. OBJECTIVE: The primary objective of this study is to improve the segmentation precision of CBCT series slice images. METHODS: This paper presents a method based on the Phansalkar to segment CBCT series slice images precisely. First, the basics of the proposed method and the necessity of changing the local window size are analysed. The adaptive accumulated Phansalkar, which collects each pixel's classification results in different local windows, is proposed. Second, the bimodal distribution of the histogram is used to calculate the appropriate local window size for each pixel adaptively. Third, the characteristics of the accumulated probability (the accumulated classification results divided by the accumulated times) are analysed, from which an adaptive method is applied to segment the accumulated probability. Last, experiments are conducted on CBCT series slice images of three workpieces and one computer-aided design (CAD) model with internal defects. RESULTS: The proposed new method can segment CBCT images with noise and beam-hardening well. Moreover, for the segmentation of all four CBCT series slice images, the new method acquired the highest BF and AOM scores (1 and 0.9981) with the smallest standard deviation (0.0013) as compared with other existing methods including CMF (continuous max-flow/min cut), MS (mean-shift), DRLSE (distance regularized level set evolution), and ARKFCM (adaptively regularized kernel-based fuzzy c-means clustering). CONCLUSIONS: The experimental results support that our new method can more precisely segment CBCT series slice images with noise and artifacts than many existing methods. Thus, the new method has prospective application value and can provide valuable technical support for the industrial CBCT image post-processing system.

Image artifacts and noise reduction algorithm for cone-beam computed tomography with low-signal projections.

This study aims to investigate and test a new image reconstruction algorithm applying to the low-signal projections to generate high quality images by reducing the artifacts and noise in the cone-beam computed tomography (CBCT). For the low-signal and noisy projections, a multiple sampling method is first utilized in projection domain to suppress environmental noise, which guarantees the accuracy of the data for reconstruction, simultaneously. Next, a fuzzy entropy based method with block matching 3D (BM3D) filtering algorithm is employed to improve the image quality to reduce artifacts and noise in image domain. Then, simulation studies on polychromatic spectrum were performed to evaluate the performance of the proposed new algorithm. Study results demonstrated significant improvement in the signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs) of the images reconstructed using the new algorithm. SNRs and CNRs of the new images were averagely 40% and 20% higher than those of the previous images reconstructed using the traditional algorithms, respectively. As a result, since the new image reconstruction algorithm effectively reduced the artifacts and noise, and produced images with better contour and grayscale distribution, it has the potential to improve image quality using the original CBCT data with the low and missing signals.

Repair of Underwater Concrete Cracks on Dam Surface: Optimization Analysis of the Grouting Process with Surface Sealing.

The grouting repair process of the sealing baffle on the surface of dam cracks can improve the repair slurry diffusion distance in the cracks; however, the process must be optimized. To address the problem of crack repair technology of underwater dam concrete with one section open and the other closed, a grouting analysis model was established. By adjusting various parameters in the grouting process, the influences of the grouting pressure, position of the grouting hole, diameter of the grouting hole, and water pressure on the diffusion of the Bingham fluid repair slurry in these cracks were studied. The results show that the grouting pressure and diameter of the grouting hole significantly influence the limited diffusion distance of Bingham fluid cement slurry in cracks. With an increase in grouting pressure and grouting hole diameter, the limiting distance of the front surface increases. The influences of the water pressure and position of the grouting hole are small. In addition, through correlation analysis, the degrees of influence of different factors can be sorted, providing the priority factors for actual operation construction.

Inhibition photooxidation of pyrite under illumination via altering photogenerated carrier migration pathways: Role of DTC-TETA surface passivation.

The oxidation of pyrite is the main cause of acidic mine drainage (AMD), which is a very serious environmental problem in numerous mining areas around the world. Previous studies have shown that passivation agents create a hydrophobic film on the surface of pyrite, effectively isolating oxygen and water. However, the presence of abundant sulfide minerals in tailings ponds may exacerbate AMD when exposed to solar radiation, due to the semiconductor properties of pyrite. It remains uncertain whether the current surface passivation coating can effectively prevent the oxidation of pyrite under light conditions. This paper is the first to investigate the passivation effect as well as the mechanism of surface passivation coating on pyrite under illumination from the perspective of materials science. The results demonstrated that the triethylenetetramine-bisdithiocarbamate (DTC-TETA) passivation coating on pyrite almost completely suppressed the photooxidation of pyrite under illumination by changing the migration path of photogenerated charge carriers. The formation of NC(S)2-Fe chelating groups provides atomic-level interface channels for DTC-TETA to transfer electrons to pyrite and creates a favorable reduction environment for pyrite. Besides, DTC-TETA coating greatly improves the electron-hole pairs recombination efficiency of pyrite, which significantly inhibits the photogenerated electron reduction of oxygen to generate reactive oxygen species (ROS). Moreover, DTC-TETA coating captures the photogenerated holes, avoiding direct oxidation of pyrite by holes. Density functional theory (DFT) calculations revealed that the DTC-TETA coating increases the adsorption energy barrier for oxygen and water. The results extend the existing knowledge on passivation mechanisms on pyrite and hold significant implications for the future screening, evaluation, and practical application of surface passivating agents.

A Novel Updated Full-Discretization Method for Prediction of Milling Stability.

This paper presents an updated full-discretization method for milling stability prediction based on cubic spline interpolation. First, the mathematical model of the time-delay milling system considering regenerative chatter is represented by a dynamic delay differential equation. Then, in a single tooth passing period, the time is divided into a finite time intervals, the state item and the time-delay item are approximated in each time interval by cubic spline interpolation and third-order Newton interpolation, respectively. Afterward, a transition matrix is constructed to represent the transfer relationship of the teeth in a period. Finally, based on Floquet theory, the milling stability lobes can be obtained. Meanwhile, in order to improve computational efficiency, an optimized method is proposed based on the traditional algorithm and the proposed method has high precision without losing high efficiency. Finally, several milling experiments are conducted to verify the accuracy of the proposed method, and the results show that the predicted results agree well with the experimental results.

Effect of Process Parameters on Tensile Mechanical Properties of 3D Printing Continuous Carbon Fiber-Reinforced PLA Composites.

Three-dimensional (3D) printing continuous carbon fiber-reinforced polylactic acid (PLA) composites offer excellent tensile mechanical properties. The present study aimed to research the effect of process parameters on the tensile mechanical properties of 3D printing composite specimens through a series of mechanical experiments. The main printing parameters, including layer height, extrusion width, printing temperature, and printing speed are changed to manufacture specimens based on the modified fused filament fabrication 3D printer, and the tensile mechanical properties of 3D printing continuous carbon fiber-reinforced PLA composites are presented. By comparing the outcomes of experiments, the results show that relative fiber content has a significant impact on mechanical properties and the ratio of carbon fibers in composites is influenced by layer height and extrusion width. The tensile mechanical properties of continuous carbon fiber-reinforced composites gradually decrease with an increase of layer height and extrusion width. In addition, printing temperature and speed also affect the fiber matrix interface, i.e., tensile mechanical properties increase as the printing temperature rises, while the tensile mechanical properties decrease when the printing speed increases. Furthermore, the strengthening mechanism on the tensile mechanical properties is that external loads subjected to the components can be transferred to the carbon fibers through the fiber-matrix interface. Additionally, SEM images suggest that the main weakness of continuous carbon fiber-reinforced 3D printing composites exists in the fiber-matrix interface, and the main failure is the pull-out of the fiber caused by the interface destruction.

[Beam hardening correction method for X-ray computed tomography based on subsection beam hardening curves].

After researching the forming principle of X-ray beam hardening and analyzing the usual methods of beam hardening correction, a beam hardening correction model was established, in which the independent variable was the projection gray, and so the computing difficulties in beam hardening correction can be reduced. By considering the advantage and disadvantage of fitting beam hardening curve to polynomial, a new expression method of the subsection beam hardening curves based on polynomial was proposed. In the method, the beam hardening data were fitted firstly to a polynomial curve which traverses the coordinate origin, then whether the got polynomial curve surged in the fore-part or back-part of the fitting range was judged based on the polynomial curvature change. If the polynomial fitting curve surged, the power function curve was applied to replace the surging parts of the polynomial curve, and the C1 continuity was ensured at the joints of the segment curves. The experimental results of computed tomography (CT) simulation show that the method is well stable in the beam hardening correction for the ideal CT images and CT images with added noises, and can mostly remove the beam hardening artifact at the same time.

Investigation of Tool Wear and Chip Morphology in Dry Trochoidal Milling of Titanium Alloy Ti-6Al-4V.

Titanium alloys are widely used in the manufacture of aircraft and aeroengine components. However, tool wear is a serious concern in milling titanium alloys, which are known as hard-to-cut materials. Trochoidal milling is a promising technology for the high-efficiency machining of hard-to-cut materials. Aiming to realize green machining titanium alloy, this paper investigates the effects of undeformed chip thickness on tool wear and chip morphology in the dry trochoidal milling of titanium alloy Ti-6Al-4V. A tool wear model related to the radial depth of cut based on the volume of material removed (VMR) is established for trochoidal milling, and optimized cutting parameters in terms of cutting speed and axial depth of cut are selected to improve machining efficiency through reduced tool wear. The investigation enables the environmentally clean rough machining of Ti-6Al-4V.

DPP-4 inhibitors for the treatment of type 2 diabetes: a methodology overview of systematic reviews.

AIMS: To evaluate the methodological quality of systematic reviews (SRs), and summarize evidence of important outcomes from dipeptidyl peptidase-4 inhibitors (DPP4-I) in treating type 2 diabetes mellitus (T2DM). METHODS: We included SRs of DPP4-I for the treatment of T2DM until January, 2018 by searching the Cochrane Library, PubMed, EMBASE and three Chinese databases. We evaluated the methodological qualities with the AMSTAR (Assessing the Methodological Quality of Systematic Reviews) tool and the GRADE (The Grading of Recommendations Assessment, Development and Evaluation) approach. RESULTS: Sixty-three SRs (a total of 2,603,140 participants) receiving DPP4-I for the treatment of T2DM were included. The results of AMSTAR showed that the lowest quality was "a list of studies (included and excluded) item" with only one (1.6%) study provided, followed by the "providing a priori design" item with only four (6.3%) studies conforming to this item, the next were "the status of publication (gray literature) used as an inclusion criterion item", with only 18 (28.9%) studies conforming to these items. Only seven (11.1%) studies scored more than nine points in AMSTAR, indicating high methodological quality. For GRADE, of the 128 outcomes, high quality evidence was provided in only 28 (21.9%), moderate in 70 (54.7%), low in 27 (21.1%), and very low in three (2.3%). CONCLUSIONS: The methodological quality of SRs of DPP4-I for type 2 diabetes mellitus is not high and there are common areas for improvement. Furthermore, the quality of evidence level is moderate and more high quality evidence is needed.

The efficacy and safety of dipeptidyl peptidase-4 inhibitors for type 2 diabetes: a Bayesian network meta-analysis of 58 randomized controlled trials.

AIMS: The aim is to evaluate the efficacy and safety of dipeptidyl peptidase-4 inhibitors (DPP4-I: sitagliptin, saxagliptin, linagliptin, vildagliptin and alogliptin) in patients with type 2 diabetes. METHODS: We searched the Cochrane Library, PubMed, EMBASE, Chinese Biomedical Database (CBM), China National Knowledge Infrastructure (CNKI), and the Wanfang Database from inception to April, 2018. Randomized controlled trials were included if they compared the different versions of DPP4-I with each other or with placebo in treatment of type 2 diabetes. Bayesian network meta-analysis and pairwise meta-analysis were performed to evaluate the efficacy and safety of the different kinds of DPP4-I and placebo. The data were analyzed using STATA 12.0 and WinBUGS1.4 software. RESULTS: We identified 58 eligible studies (with 31356 patients) involving 14 treatment arms. Indirect comparison results showed that except for alogliptin, a decrease was found for all DPP4-I versus the placebo for hemoglobin A1c (HbA1c) with vildagliptin50 twice daily (BID) showing the highest probability. Linagliptin5 once daily (QD) decreased the level of fasting plasma glucose (FPG) the most for all DPP4-I versus the placebo; when comparing them with each other, alogliptin25QD was more effective when compared with sitagliptin100QD and vildaglipti50BID; linagliptin5qd had the highest decrease impact on body mass index (BMI). Except for hypoglycemia and upper respiratory tract infection (URTI), there are no statistical significance on incidence of adverse events and the body weight when DPP4-I are compared with each other or with placebo. CONCLUSION: Our network meta-analysis presents the associations of DPP4-I versus placebos on HbA1c, FPG, 2 h postprandial blood glucose (2HPPG), BMI, body weight and adverse events. DPP4-I have a lowering effect on the glycemic level (HbA1c, FPG), especially vildaglipti50BID and linagliptin10QD, respectively. Besides, linagliptin5QD has the greatest probabilities of reducing BMI. In addition, DPP4-I were associated with not increasing the incidence of adverse events. Among them, vildagliptin100QD and sitagliptin100QD have the lowest probability in reducing the incidence of hypoglycemia and URTI, respectively.

[Use of digital image correlation method to measure polymerization shrinkage dynamics of light cured composite resin].

PURPOSE: To evaluate the role of digital image correlation method in measuring the initiation and propagation of polymerization shrinkage of light cured composite resin. METHODS: Six freshly extracted complete molars were collected and divided into 2 groups randomly. The proximal surface was sliced to plane and proximal-occlusal cavity were prepared with 2.0 mm×2.0 mm×2.0 mm in size, then the tissue surface was treated with etch and bond. The cavity samples in the first group were filled with 3M Z350, and the samples in the second group were filled with material 3M Valux Plus, the proximal surfaces were dealt with random speckle, then fixed to micro tensile framework. As light curing proceeded for 40 seconds, all the speckled images were collected by digital camera in real-time simultaneously. The digital image correlation analysis software was used to deal these images and achieve the displacement and strains in both horizontal and vertical direction on all pixel points, at last the linear shrinkage ratios were counted and the displacement at free surface of the two materials at the 20th second were analyzed with SPSS 12.01 software package for Student's t test. RESULTS: The results showed displacement and strain distribution were accurately achieved and their correlation ratios (R) were bigger than 0.98. The shrinkage represented anisotropy with different direction and unequal value in 40 seconds. The linear shrinkage values of the two materials were 0.439%-0.75%, 0.526%-0.834% in horizontal direction and 0.253%-1.34%, 0.355%-1.51% in vertical direction,respectively. Considering the displacement at the 20th second, shrinkage of Z350 was lower than V. P's both in horizontal and vertical directions (P<0.05). CONCLUSIONS: This study indicates that digital image correlation method can be used to study the polymerization shrinkage of light-cured composites kinematically and effectively, and calculate displacement and strain continually in full fields. Also this method is much closer to clinic application, and can give more theoretical and experimental evidence for clinic use.

[Phosphorus characteristics in rhizosphere soil of Cunninghamia lanceolata, Pinus massoniana and their mixed plantations].

In 2007-2010, a comparative study was conducted on the phosphorus characteristics in the rhizosphere soil of Cunninghamia lanceolata, Pinus massoniana and C. lanceolata-P. massoniana mixed plantations in a forest farm in Nanping City of Fujian Province, East China. In the rhizosphere soil of pure C. lanceolata and P. massoniana plantations, the content of available P was higher than that in non-rhizosphere soil. As compared with non-rhizosphere soil, the rhizophere soil in the three plantations had lower pH and O-P content but higher Al-P and Fe-P contents, and its P adsorption capacity was lower while the P desorption rate and desorbed P were in adverse. In the rhizophere soil of pure P. massoniana plantation, the contents of available P, Fe-P, and Al-P, their desorption rates, and desorption capacity were higher, but the O-P content and the adsorbed P were lower, as compared with those in the rhizophere soil of pure C. lanceolata plantation. In the mixed plantation, the P activation in rhizophere soil was further improved, being more obvious under C. lanceolata, which suggested that mixed plantation of C. lanceolata and P. massoniana could promote the phosphorus nutrition of C. lanceolata.

[Application of digital photography in color matching of porcelain restoration in special color teeth].

PURPOSE: To evaluate the clinical application of digital photography in special color teeth, and to explore the role and the problems s of digital photos to improve cosmetic effect. METHODS: Digital photography combined visual color-matching was applied in 50 cases with special color teeth in ceramic restorations selected randomly. Then the satisfactory degree of the patients and dentists was evaluated and the value of L*a*b* between prosthesis and its neighbors was collected by self-developed software Dental ImgShop. Chroma (C(ab) )and hue (h(ab) degrees ) were calculated according to the value of a and b. The data was analyzed with paired t test using SAS6.12 software package, so as chromatic aberration (deltaE). RESULTS: The satisfactory degree of the patients was 98%, and the satisfaction degree of the dentists was 94%. The range of L, a ,b C(ab), h(ab) degrees of special color teeth was 54.50-92.29, -0.97-8.12,-0.73-20.85,0.85-21.34,29.73-89.20, respectively. There was no significant difference between the prosthesis and their neighbors statistically (P>0.05). The mean value of chromatic aberration (deltaE) was 0.948(0.136-3.45), and only 3 cases were unacceptable (deltaE>/=2). CONCLUSIONS: Digital photography could record and transmit the color information of special color teeth more exactly, and could improve the patients satisfaction and the cosmetic effect in color measuring. Supported by Research Fund of Natural Science for Young Scholars of Minhang Central Hospital.

[Change of moisture retention in sandy soil after planting mixed forest of Populus spp. and Robinia pseudoacacia].

The change of soil moisture retention after planting mixed forest of Populus spp. and Robinia pseudoacacia was studied by comparative method. The results showed that soil moisture retention, spatial distribution of soil pore, and soil water capacity were improved and increased in sandy soil after Populus spp. and Robinia pseudoacacia being planted, and the improvement in the mixed forest of Populus spp. and R. pseudoacacia was greater than that in the pure forest of Populus spp. or R. pseudoacacia. The basic reason of soil moisture retention being improved was the increment of soil organic matter, which improved soil pore condition.