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1.
The objective of the present research is to investigate the relationship among tool wear, surface topography, and surface roughness when high-speed end milling Ti-6Al-4V alloy, and also to define an optimal flank wear criterion for the cutting tool to integrate tool life and the surface roughness requirements of the finish milling process. An annealed Ti-6Al-4V alloy was selected as the workpiece material, undergoing end milling with uncoated carbide inserts. The flank wear of the insert was observed and measured with the toolmaker's microscope. To examine machined surfaces, 3D surface topography was provided by the white light interferometer, and the arithmetical mean roughness (Ra) was calculated with the WYKO Vision32 software. The flank wear increases with cutting time, and the maximal flank wear is set as the flank wear criterion. As the cutting process progresses, tool wear is the predominant factor affecting the variation of surface roughness. According to the plots for the tool wear propagation and surface roughness variation, an optimal flank wear criterion can be defined which integrates the tool life and the surface roughness requirements for the finish milling process.  相似文献   

2.
In this paper, a series of experiments were performed by high speed milling of Ti-6.5Al-2Zr-1Mo-1V (TA15) by use of polycrystalline diamond (PCD) tools. The characteristics of high speed machining (HSM) dynamic milling forces were investigated. The effects of the parameters of the process, i.e., cutting speed, feed per tooth, and depth of axial cut, on cutting forces were studied. The cutting force signals under different cutting speed conditions and different cutting tool wear stages were analyzed by frequency spectrum analysis. The trend and frequency domain aspects of the dynamic forces were evaluated and discussed. The results indicate that a characteristic frequency in cutting force power spectrum does in fact exist. The amplitudes increase with the increase of cutting speed and tool wear level, which could be applied to the monitoring of the cutting process.  相似文献   

3.
To investigate cutting performance in the helical milling of carbon fiber reinforced polymer (CFRP), experiments were conducted with unidirectional laminates. The results show that the influence of cutting parameters is very significant in the helical milling process. The axial force increases with the increase of cutting speed, which is below 95 m/min; otherwise, the axial force decreases with the increase of cutting speed. The resultant force always increases when cutting speed increases; with the increase of tangential and axial feed rates, cutting forces increase gradually. In addition, damage rings can appear in certain regions of the entry edges; therefore, the relationship between machining performance (cutting forces and hole-making quality) and cutting parameters is established using the nonlinear fitting methodology. Thus, three cutting parameters in the helical milling of CFRP, under the steady state, are optimized based on the multi-objective genetic algorithm, including material removal rate and machining performance. Finally, experiments were carried out to prove the validity of optimized cutting parameters.  相似文献   

4.
In this work, the orthogonal cutting experiments on Ti-6Al-4V alloy were conducted at different cutting speeds(10—160 m/min)and feed rates(20—160 μm/rev). The tool-chip contact length was measured by the track of tool rake face; meanwhile, the chip morphology caused by the localized and overall chip deformation was characterized by the degree of segmentation and the chip compression ratio, respectively. These parameters were analyzed and calculated according to the segmented chip morphology. In addition, three modified models considering the overall chip deformation and the localized deformation of adiabatic shear band were proposed, and the constants of the models were calculated by the genetic algorithm optimization. Considering the overall and localized chip deformation, the value and variation trend of the tool-contact length predicted by these three models agreed well with the experimental results.  相似文献   

5.
Aiming at the surface integrity of titanium alloy Ti-6Al-4V in high speed side milling, a series of side mill- ing tests were carried out with uncoated carbide milling cutter at various milling speeds. Surface roughness, residual stress, subsurface microstructure and microhardness variations were investigated. The surface roughness measurement results present that the milling speed from 80 to 120 m/min fails to produce better and more stable roughness values compared with the result obtained from 320 to 380 m/min. The residual stresses in the feed direction and axial depth of cut direction are in similar trends for the two milling speed levels mentioned above. Moreover, the residual stress pro- duced at 320 to 380 m/min is lower and more stable than that at 80 to 120 m/min. The microstructure analysis shows that the volume of β phase in the near surface becomes smaller and the deformation of β phase in the near surface be- comes obvious with the increase of the milling speed. Subsurface microhardness variation was observed down to 200 μm below the machined surface at 80 to 120 m/min and down to 160 μm at 320 to 380 m/min. It is concluded that better surface integrity and higher material removal rate can be obtained at 320 to 380 m/min than at 80 to 120 m/min.  相似文献   

6.
Stress equilibrium equations, boundary-and continuity-conditions were used to establish a theoretical model of progressive debonding with friction at the debonded interface. On a basis of the minimum complementary energy principle, an expression for the energy release rateG was derived to explore the interfacial fracture properties. An interfacial debonding criterionGΓ i was introduced to determine the critical debond length and the bridging law. Numerical calculation results for fiber-reinforced composite SCS-6/Ti-6A1-4V were compared with those obtained by using the shear-lag models.  相似文献   

7.
An appraisal of techniques and equipment for cutting force measurement   总被引:2,自引:0,他引:2  
INTRODUCTION Metal machining processes are characterised mainly by quick changes in quantified elements. In- dividual changes do not occur in isolation and they influence each other. The analysis of these changes require study of the complicated complete systems in their real situations. The study of cutting processes such as turning and facing, from dynamic aspects, is very important. The trend towards the measurement of cutting forces in machining leads to many theo- retical and practic…  相似文献   

8.
A near infrared spectroscopy (NIRS) approach was established for quality control of the alcohol precipitation liquid in the manufacture of Codonopsis Radix. By applying NIRS with multivariate analysis, it was possible to build variation into the calibration sample set, and the Plackett-Burman design, Box-Behnken design, and a concentrating-diluting method were used to obtain the sample set covered with sufficient fluctuation of process parameters and extended concentration information. NIR data were calibrated to predict the four quality indicators using partial least squares regression (PLSR). In the four calibration models, the root mean squares errors of prediction (RMSEPs) were 1.22 μg/ml, 10.5 μg/ml, 1.43 μg/ml, and 0.433% for lobetyolin, total flavonoids, pigments, and total solid contents, respectively. The results indicated that multi-components quantification of the alcohol precipitation liquid of Codonopsis Radix could be achieved with an NIRS-based method, which offers a useful tool for real-time release testing (RTRT) of intermediates in the manufacture of Codonopsis Radix.  相似文献   

9.

Objective

To investigate the effects of corneal thickness distribution and apex position on postoperative refractive status after full-bed deep anterior lamellar keratoplasty (FBDALK).

Methods

This is a retrospective analysis of patients who were diagnosed with advanced keratoconus between 2011 and 2014 in our hospital. The base of the cone in all patients did not exceed the central cornea at a 6-mm range. The FBDALK was performed by a same surgeon. All patients had a complete corneal suture removal and the follow-up records were intact. Patients who had graft-bed misalignment or who were complicated with a cataract or glaucoma were excluded. Uncorrected visual acuity (UCVA), best spectacle corrected visual acuity (BSCVA), and Pentacam examination data were recorded at two years postoperatively. The recorded data included the superior-inferior (S-I) and nasal-temporal (N-T) corneal thickness differences in 2, 4, 6, and 8 mm diameter concentric circles with the corneal apex as the center (S-I2 mm, S-I4 mm, S-I6 mm, S-I8 mm, N-T2 mm, N-T4 mm, N-T6 mm, and N-T8 mm), the linear, X-axis, and Y-axis distance between the corneal pupillary center and the cornea apex, total corneal astigmatism at a zone of 3 mm diameter from the corneal apex (TA3 mm), the astigmatic vector values J0 and J45, and the corneal total higher-order aberration for 3 and 6 mm pupil diameters (HOA3 mm and HOA6 mm). Statistical analysis was performed by SPSS 15.0.

Results

A total of 47 eyes of 46 patients met the criteria and were included in this study. The mean follow-up time was (28±7) months. The mean UCVA was 0.45±0.23 (logMAR) (MAR: minimum angle of resolution) and the mean BSCVA was 0.19±0.15 (logMAR), which were all significantly positively correlated with postoperative TA3 mm and HOA3 mm. The mean S-I corneal thickness differences were (44.62±37.74) μm, and the mean N-T was (38.57±32.29) μm. S-I2 mm was significantly positively correlated with J0 (r=0.31), J45 (r=0.42), HOA3 mm (r=0.37), and HOA6 mm (r=0.48). S-I4 mm and S-I8 mm were significantly positively correlated with HOA3 mm (r=0.30, r=0.40) and HOA6 mm (r=0.46, r=0.35). The X-axis distance between corneal pupillary center and corneal apex was significantly positively correlated with J45 (r=0.29).

Conclusions

In patients with advanced keratoconus after FBDALK, the unevenly distributed thickness at corneal pupillary area and the misalignment of corneal apex and pupillary center might cause significant regular and irregular astigmatism, which affected the postoperative visual quality.
  相似文献   

10.
11.

Objectives

This study aimed to compare the learning curves of percutaneous endoscopic lumbar discectomy (PELD) in a transforaminal approach at the L4/5 and L5/S1 levels.

Methods

We retrospectively reviewed the first 60 cases at the L4/5 level (Group I) and the first 60 cases at the L5/S1 level (Group II) of PELD performed by one spine surgeon. The patients were divided into subgroups A, B, and C (Group I: A cases 1–20, B cases 21–40, C cases 41–60; Group II: A cases 1–20, B cases 21–40, C cases 41–60). Operation time was thoroughly analyzed.

Results

Compared with the L4/5 level, the learning curve of transforaminal PELD at the L5/S1 level was flatter. The mean operation times of Groups IA, IB, and IC were (88.75±17.02), (67.75±6.16), and (64.85±7.82) min, respectively. There was a significant difference between Groups A and B (P<0.05), but no significant difference between Groups B and C (P=0.20). The mean operation times of Groups IIA, IIB, and IIC were (117.25±13.62), (109.50±11.20), and (92.15±11.94) min, respectively. There was no significant difference between Groups A and B (P=0.06), but there was a significant difference between Groups B and C (P<0.05). There were 6 cases of postoperative dysesthesia (POD) in Group I and 2 cases in Group IIA (P=0.27). There were 2 cases of residual disc in Group I, and 4 cases in Group II (P=0.67). There were 3 cases of recurrence in Group I, and 2 cases in Group II (P>0.05).

Conclusions

Compared with the L5/S1 level, the learning curve of PELD in a transforaminal approach at the L4/5 level was steeper, suggesting that the L4/5 level might be easier to master after short-term professional training.
  相似文献   

12.

Objective

Salmonella enterica remains a major cause of food-borne disease in humans, and Salmonella Typhimurium (ST) contamination of poultry products is a worldwide problem. Since macrophages play an essential role in controlling Salmonella infection, the aim of this study was to evaluate the effect of glycyrrhizic acid (GA) on immune function of chicken HD11 macrophages.

Methods

Chicken HD11 macrophages were treated with GA (0, 12.5, 25, 50, 100, 200, 400, or 800 μg/ml) and lipopolysaccharide (LPS, 500 ng/ml) for 3, 6, 12, 24, or 48 h. Evaluated responses included phagocytosis, bacteria-killing, gene expression of cell surface molecules (cluster of differentiation 40 (CD40), CD80, CD83, and CD197) and antimicrobial effectors (inducible nitric oxide synthase (iNOS), NADPH oxidase-1 (NOX-1), interferon-γ (IFN-γ), LPS-induced tumor necrosis factor (TNF)-α factor (LITAF), interleukin-6 (IL-6), and IL-10), and production of nitric oxide (NO) and hydrogen peroxide (H2O2).

Results

GA increased the internalization of both fluorescein isothiocyanate (FITC)-dextran and ST by HD11 cells and markedly decreased the intracellular survival of ST. We found that the messenger RNA (mRNA) expression of cell surface molecules (CD40, CD80, CD83, and CD197) and cytokines (IFN-γ, IL-6, and IL-10) of HD11 cells was up-regulated following GA exposure. The expression of iNOS and NOX-1 was induced by GA and thereby the productions of NO and H2O2 in HD11 cells were enhanced. Notably, it was verified that nuclear factor-κB (NF-κB) and c-Jun N-terminal kinase (JNK) pathways were responsible for GA-induced synthesis of NO and IFN-γ gene expression.

Conclusions

Taken together, these results suggested that GA exhibits a potent immune regulatory effect to activate chicken macrophages and enhances Salmonella-killing capacity.
  相似文献   

13.
(R)-2-hydroxy-3-phenylpropionic acid (PLA) is an ideal antimicrobial compound with broad-spectrum activity against a wide range of Gram-positive bacteria, some Gram-negative bacteria, and fungi. We studied the bioconversion of phenylpyruvate (PPA) to PLA using whole recombinant Escherichia coli cells in a series of buffer/organic solvent systems. Octane was found to be the best organic solvent. The optimum volume ratio of the water phase to the n-octane phase, conversion temperature, substrate concentration, and cell concentration were 6:4, 40 °C, 12.5 g/L, and 30 g/L wet cells, respectively. Under the optimized conditions, the average PLA productivity in the aqueous/n-octane system was 30.69% higher than that in the aqueous system, and 32.31 g/L PLA was obtained with the use of a stirred reactor (2-L scale). Taken together, our findings indicated that PLA biosynthesis was more efficient in an aqueous/n-octane biphasic system than in a monophasic aqueous system. The proposed biphasic system is an effective strategy for enhancing PLA yield and the biosynthesis of its analogues.  相似文献   

14.
The transition to university appears to be a complex and delicate time in students’ lives, involving a sequence of changes regarding both the personal/affective and social/professional spheres, facilitating students’ ability to adapt to a new life context. It represents a challenging time that requires students to use adaptive resources to face many changes, including a new academic environment (Park and Adler Health Psychology, 22(6), 627, 2003; Anderson et al. International Journal of Educational Research, 33(4), 325–339, 2000). This paper presents an investigation that focuses on Italian students in transition to university to assess existing gender and age differences in coping strategies and optimism. Furthermore, the study also was designed to explore the impact that coping strategies and optimism have on students’ life satisfaction. The sample consists of 298 first-year undergraduate Italian students enrolled in social science courses at the University of Cagliari (Sardinia): 152 (51%) were female and 146 (49%) were male. The ages of the participants ranged from 18 to 37 years, with a mean age of 23.2 years (SD = 3.9) The statistical analysis revealed a strong influence from optimism and coping strategies on life satisfaction, as well as an important role played by both gender and age in shaping students’ coping strategies, optimism, and life satisfaction. This research could contribute to helping students better face this life transition, thereby increasing life satisfaction and class-attendance levels, improving academic performance, and reducing the number of university dropouts.  相似文献   

15.
The aim of this study was to research the changes in cytotoxicity and antibacterial properties after silver nanoparticles (AgNPs) were incorporated into the surface coating of dental alloys. AgNPs were attached to cobalt chromium alloys and pure titanium using a hydrothermal method, according to the reaction: AgNO3+NaBH4→ Ag+1/2H2+1/2B2H6+NaNO3. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay was used to evaluate the cytotoxicity of the alloys when in contact with osteogenic precursor cells (MC3T3-E1) from mice and mesenchymal stem cells (BMSC) from rats. The antibacterial properties of dental alloys incorporating three different concentrations (10, 4, and 2 μmol/L) of AgNPs were tested on Staphylococcus aureus (SA) and Streptococcus mutans (MS). High cytotoxicity values were observed for all dental alloys that contained 0% of AgNPs (the control groups). The incorporation of AgNPs reduced cytotoxicity values. No significant difference was observed for antibacterial performance when comparing dental alloys containing AgNPs to the respective control groups. The results demonstrated that the cobalt chromium alloys and pure titanium all had cytotoxicity to MC3T3-E1 and BMSC and that the incorporation of AgNPs could reduce this cytotoxicity. The concentrations of AgNPs adopted in this study were found to have no antibacterial action against SA or MS.  相似文献   

16.
The aim of this study was to evaluate the possible therapeutic or protective effects of Helichrysum plicatum DC. subsp. plicatum ethanol extract (HPE) against gentamicin-induced nephrotoxicity. Thirty-six Sprague Dawley male rats weighing between 200 and 250 g were used as live material. They were formed into six groups containing 6 rats each and were allowed to adapt to laboratory conditions for 7 d. Group I: control, 5% DMSO intraperitoneal (i.p.); Group II: HPE 100 mg/(kg·d) i.p.; Group III: HPE 200 mg/(kg·d) i.p.; Group IV: gentamicin as 80 mg/(kg·d) i.p.; Group V: gentamicin as 80 mg/(kg·d) i.p.+HPE 100 mg/(kg·d) i.p.; and Group VI: gentamicin as 80 mg/(kg·d) i.p.+HPE 200 mg/(kg·d) i.p. for 8 d. Following treatment, serum, liver, and kidney tissues were used to assess blood urea nitrogen (BUN), creatinine, enzymatic and non-enzymatic antioxidants, and lipid peroxidation. Gentamicin significantly increased serum BUN, creatinin, and liver and kidney levels of malondialdehyde (MDA). It also decreased the activity of catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD). Treatment with the HPE 100 mg/kg reversed gentamicin-induced alterations as evidenced by decreased serum BUN and creatinin, liver and kidney oxidant marker, and tubular necrosis as well as by an increase in antioxidant enzymes. It was found that HPE 200 mg/kg significantly increased liver and kidney tissue MDA levels in nephrotoxicity in rats. As a result, these findings support the proposition that HPE in 100 mg/kg dose demonstrates in the kidney and liver as free radicals and scavenger to prevent the toxic effects of gentamicin in both the biochemical and histopathology parameters.  相似文献   

17.

Objective

Fentanyl-induced cough (FIC) is a common complication with a reported incidence from 18.0% to 74.4% during general anesthesia induction. FIC increases the intrathoracic pressure and risks of postoperative nausea and vomiting, yet available treatments are limited. This study was designed to investigate whether administering fentanyl via a slow intravenous fluid line can effectively alleviate FIC during induction of total intravenous general anesthesia.

Methods

A total number of 1200 patients, aged 18–64 years, were enrolled, all of whom were American Society of Anesthesiologists (ASA) grade I or II undergoing scheduled surgeries. All patients received total intravenous general anesthesia, which was induced sequentially by midazolam, fentanyl, propofol, and cisatracurium injection. Patients were randomly assigned to receive fentanyl 3.5 μg/kg via direct injection (control group) or via a slow intravenous fluid line. FIC incidence and the severity grades were analyzed with the Mann-Whitney test. Other adverse reactions, such as hypotension, hypertension, bradycardia, tachycardia, hypoxemia, vomiting, and aspiration, during induction were also observed. The online clinical registration number of this study was ChiCTR-IOR-16009025.

Results

Compared with the control group, the incidence of FIC was significantly lower in the slow intravenous fluid line group during induction (9.1%, 95% confidence interval (CI): 6.7%–11.4% vs. 55.9%, 95% CI: 51.8%–60.0%, P=0.000), as were the severity grades (P=0.000). There were no statistical differences between the two groups with regard to other adverse reactions (P>0.05).

Conclusions

The administration of fentanyl via a slow intravenous fluid line can alleviate FIC and its severity during induction for total intravenous general anesthesia. This method is simple, safe, and reliable, and deserves clinical expansion.
  相似文献   

18.
Climate change is one of the most challenging problems facing today’s global society (e.g., IPCC 2013). While climate change is a widely covered topic in the media, and abundant information is made available through the internet, the causes and consequences of climate change in its full complexity are difficult for individuals, especially non-scientists, to grasp. Science education is a field which can play a crucial role in fostering meaningful education of students to become climate literate citizens (e.g., NOAA 2009; Schreiner et al., 41, 3–50, 2005). If students are, at some point, to participate in societal discussions about the sustainable development of our planet, their learning with respect to such issues needs to be supported. This includes the ability to think critically, to cope with complex scientific evidence, which is often subject to ongoing inquiry, and to reach informed decisions on the basis of factual information as well as values-based considerations. The study presented in this paper focused on efforts to advance students in (1) their conceptual understanding about climate change and (2) their socioscientific reasoning and decision making regarding socioscientific issues in general. Although there is evidence that “knowledge” does not guarantee pro-environmental behavior (e.g. Schreiner et al., 41, 3–50, 2005; Skamp et al., 97(2), 191–217, 2013), conceptual, interdisciplinary understanding of climate change is an important prerequisite to change individuals’ attitudes towards climate change and thus to eventually foster climate literate citizens (e.g., Clark et al. 2013). In order to foster conceptual understanding and socioscientific reasoning, a computer-based learning environment with an embedded concept mapping tool was utilized to support senior high school students’ learning about climate change and possible solution strategies. The evaluation of the effect of different concept mapping scaffolds focused on the quality of student-generated concept maps, as well as on students’ test performance with respect to conceptual knowledge as well as socioscientific reasoning and socioscientific decision making.  相似文献   

19.
Energy is considered both a core idea and a crosscutting concept in science education. A thorough understanding of the energy concept is thought to help students learn about other (related) concepts within and across science subjects, thereby fostering scientific literacy. This study investigates students’ progression in understanding the energy concept in biological contexts at the transition from primary to lower secondary school by employing a quantitative, cross-sectional study in grades 3–6 (N?=?540) using complex multiple-choice items. Based on a model developed in a previous study, energy concepts were assessed along four aspects of energy: (1) forms and sources of energy, (2) transfer and transformation, (3) degradation and dissipation, and (4) energy conservation. Two parallel test forms (A and B) indicated energy concept scores to increase significantly by a factor of 2.3 (A)/1.7 (B) from grade 3 to grade 6. Students were observed to progress in their understanding of all four aspects of the concept and scored highest on items for energy forms. The lowest scores and the smallest gain across grades were found for energy conservation. Based on our results, we argue that despite numerous learning opportunities, students lack a more integrated understanding of energy at this stage, underlining the requirement of a more explicit approach to teaching energy to young learners. Likewise, more interdisciplinary links for energy learning between relevant contexts in each science discipline may enable older students to more efficiently use energy as a tool and crosscutting concept with which to analyze complex content.  相似文献   

20.
Early intervention is critical for improved prognosis and quality of life for young children with developmental delays and disabilities. Yet, disparities persist among underserved families with young children. These disparities include knowledge of child development, use of medical providers as referral sources, and later diagnosis. The current study employed a mixed method, randomized controlled trial to examine participant outcomes among low-income, underserved families who received child development information. The information included the 42-page Milestone Moments booklet that was developed by the Centers for Disease Control and Prevention’s Learn the Signs/Act Early initiative. Participants (n = 108) included parents or legal guardians of children ages birth through 5 years. The participants were predominantly Black/African American (86 %) and female (90 %), and all had incomes below the federal poverty level. Study variables related to the location (home vs. child care center) and context (single session vs. extended visits) for delivering the information did not yield significant differences. Yet, there were clear findings that parents who received the booklet reported increased knowledge about child development, a decrease in concern about their own children’s developmental progress, and a positive perception of the booklet. On interview, parents reported learning new information about child development or being reminded of developmental information they had forgotten and the importance of following up with professionals when concerns arose. While not statistically significant, there was a consistent trend toward greater participant outcomes for parents who received materials in the child care setting relative to the home.  相似文献   

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