Haiqing Zhang

Wear patterns and mechanisms of cutting tools in high-speed face milling

Abstract High-speed machining has received important interest because it leads to an increase of productivity and a better workpiece surface quality. However, at high cutting speeds, the tool wear increases dramatically due to the high temperature at the tool–workpiece interface. Tool wear impairs the surface finish and hence the tool life is reduced. That is why an important objective of metal cutting research has been the assessment of tool wear patterns and mechanisms. In this paper, the wear performances of PCBN tool, ceramic tool, coated carbide tool and fine-grained carbide tool in high-speed face milling are presented when cutting cast iron, 45# tempered carbon steel and 45# hardened carbon steel. The tool wear patterns were examined through a toolmaker’s microscope. The research results show that the tool wear types differed in various matching of materials between the cutting tool and the workpiece. The dominant wear patterns observed were rake face wear, flank wear, chipping, fracture and breakage. The main wear mechanisms were mechanical friction, adhesion, diffusion and chemical wear promoted by cutting forces and high cutting temperature. Hence, the important considerations of high-speed cutting tool materials are high heat-resistance and wear-resistance, and chemical stability as well as resistance to the failure of coatings. The research results will be of great benefit in the design and the selection of tool materials and in the control of tool wear in high-speed machining processes.

Adaptive fuzzy control system of a servomechanism for electro-discharge machining combined with ultrasonic vibration

Abstract For electro-discharge machining (EDM), only when in the optimum state can the highest material removal rate be realized. In the practical machining process, the timely elevation of the tool electrode, which ordinarily occupies quite a lot of time, is needed to eliminate chipping. In this paper, an adaptive fuzzy control system of a servomechanism for EDM combined with ultrasonic vibration is studied. This control system can adjust the discharge pulse parameters in a timely manner, and also the gap between the tool electrode and the workpiece material, therefore, the machining state can be optimal, by which the EDM combined with ultrasonic vibration is improved and the machining efficiency is increased. In addition, a stimulation program is designed by means of Microsoft Visual Basic software.

Thyroid-stimulating hormone regulates hepatic bile acid homeostasis via SREBP-2/HNF-4α/CYP7A1 axis

BACKGROUND & AIMS Bile acids (BAs) play a crucial role in dietary fat digestion and in the regulation of lipid, glucose, and energy metabolism. Thyroid-stimulating hormone (TSH) is a hormone produced by the anterior pituitary gland that directly regulates several metabolic pathways. However, the impact of TSH on BA homeostasis remains largely unknown. METHODS We analyzed serum BA and TSH levels in healthy volunteers under strict control of caloric intake. Thyroidectomized rats were administered thyroxine and injected with different doses of TSH. Tshr(-/-) mice were supplemented with thyroxine, and C57BL/6 mice were injected with Tshr-siRNA via the tail vein. The serum BA levels, BA pool size, and fecal BA excretion rate were measured. The regulation of SREBP-2, HNF-4α, and CYP7A1 by TSH were analyzed using luciferase reporter, RNAi, EMSA, and CHIP assays. RESULTS A negative correlation was observed between the serum levels of TSH and the serum BA levels in healthy volunteers. TSH administration led to a decrease in BA content and CYP7A1 activity in thyroidectomized rats supplemented with thyroxine. When Tshr was silenced in mice, the BA pool size, fecal BA excretion rate, and serum BA levels all increased. Additionally, we found that HNF-4α acts as a critical molecule through which TSH represses CYP7A1 activity. We further confirmed that the accumulation of mature SREBP-2 protein could impair the capacity of nuclear HNF-4α to bind to the CYP7A1 promoter, a mechanism that appears to mediate the effects of TSH. CONCLUSIONS TSH represses hepatic BA synthesis via a SREBP-2/HNF-4α/CYP7A1 signaling pathway. This finding strongly supports the notion that TSH is an important pathophysiological regulator of liver BA homeostasis independently of thyroid hormones.

Association between thyroid hormones and body fat in euthyroid subjects

Thyroid hormones disorders are associated with changes of body composition. However, the relationship between thyroid hormones and body fat in a euthyroid population is unclear. The aim of this study was to explore the association between thyroid hormones and body fat in a euthyriod population.

Follicle-Stimulating Hormone Increases the Risk of Postmenopausal Osteoporosis by Stimulating Osteoclast Differentiation.

Objective The objectives of this study were to observe the changes in follicle-stimulating hormone (FSH) and bone mineral density (BMD) in postmenopausal women, to research the relationship between FSH and postmenopausal osteoporosis, and to observe the effects of FSH on osteoclast differentiation in RAW264.7 cells. Methods We analyzed 248 postmenopausal women with normal bone metabolism. A radioimmunoassay (RIA) was used to detect serum FSH, luteinizing hormone (LH), and estradiol (E2). Dual-energy X-ray absorptiometry was used to measure forearm BMD. Then, we analyzed the age-related changes in serum FSH, LH and E2. Additionally, FSH serum concentrations were compared between a group of postmenopausal women with osteoporosis and a control group. Osteoclasts were induced from RAW264.7 cells in vitro by receptor activator of nuclear factor kappa B ligand (RANKL), and these cells were treated with 0, 5, 10, and 20 ng/ml FSH. After the osteoclasts matured, tartrate-resistant acid phosphatase (TRAP) staining was used to identify osteoclasts, and the mRNA expression levels of genes involved in osteoclastic phenotypes and function, such as receptor activator of NF-κB (Rank), Trap, matrix metalloproteinase-9 (Mmp-9) and Cathepsin K, were detected in different groups using real-time PCR (polymerase chain reaction). Results 1. FSH serum concentrations in postmenopausal women with osteoporosis increased notably compared with the control group. 2. RANKL induced RAW264.7 cell differentiation into mature osteoclasts in vitro. 3. FSH increased mRNA expression of genes involved in osteoclastic phenotypes and function, such as Rank, Trap, Mmp-9 and Cathepsin K, in a dose-dependent manner. Conclusions The circulating concentration of FSH may play an important role in the acceleration of bone loss in postmenopausal women. FSH increases osteoclastogenesis in vitro.

The relationship between endogenous testosterone and lipid profile in middle-aged and elderly Chinese men

OBJECTIVE To evaluate the relationship between serum total testosterone (TT) level and lipid profile after adjusting for some traditional confounding factors, free thyroid hormones and TSH in Chinese men. METHODS This was a retrospective study based on an epidemiological investigation including 11 000 subjects. Bivariate and partial correlation analysis, multiple linear regression analysis, and a general linear model were used to assess the influence of TT on the lipid profile. Additionally, the odds ratios (ORs) (95% CIs) for hypertriglyceridemia and low HDL-C in relation to TT categories were calculated using logistic regression analysis. RESULTS A total of 4114 subjects whose mean age was 56.04±8.75 years were finally analyzed. There was a significant linear trend toward lower total cholesterol (TC), lower triglycerides (TG), and higher HDL-C with increasing serum TT, which remained significant after adjusting for age, BMI, fasting blood glucose, systolic blood pressure, free triiodothyronine, free thyroxine, and TSH. Compared with the bottom quartile of TT, the adjusted OR (95% CI) for hypertriglyceridemia and low HDL-C was 0.082 (0.048-0.138, P=0.000) and 0.669 (0.503-0.891, P=0.006) respectively in the top quartile of TT. CONCLUSIONS TT was correlated negatively and linearly with TC, TG, and LDL-C and positively and linearly with HDL-C. Low TT might have adverse effects on the lipid profile and thus represent a risk factor for hypercholesterolemia, hypertriglyceridemia, high LDL-C, and low HDL-C, suggesting the importance of maintaining an appropriate TT level in men.

Chronic ethanol consumption increases the levels of chemerin in the serum and adipose tissue of humans and rats

Aim:Chemerin is a new adipokine involved in adipogenesis and insulin resistance. Since ethanol affects the insulin sensitivity that is closely associated with adipokines. The aim of this study was to investigate the effects of ethanol on chemerin in humans and rats.Methods:In the human study, 148 men who consumed alcohol for more than 3 years and 55 men who abstained from alcohol were included. Based on ethanol consumption per day, the drinkers were classified into 3 groups: low-dose (<15 g/d), middle-dose (15–47.9 g/d) and high-dose (≥48 g/d). Anthropometric measurements and serum parameters were collected. In the rat study, 27 male Wistar rats were randomly divided into 4 groups administered water or ethanol (0.5, 2.5, or 5 g·kg-1·d-1) for 22 weeks. The chemerin levels in the sera, visceral adipose tissue (VAT) and liver were measured using ELISA.Results:In the high-dose group of humans and middle- and high-dose groups of rats, chronic ethanol consumption significantly increased the serum chemerin level. Both the middle- and high-dose ethanol significantly increased the chemerin level in the VAT of rats. In humans, triglyceride, fasting glucose, insulin and HOMA-IR were independently associated with chemerin. In rats, the serum chemerin level was positively correlated with chemerin in the VAT after adjustments for the liver chemerin (r=+0.768). High-dose ethanol significantly increased the body fat in humans and the VAT in rats.Conclusion:Chronic ethanol consumption dose-dependently increases the chemerin levels in the serum and VAT. The serum chemerin level is associated with metabolic parameters in humans. The increased serum chemerin level is mainly attributed to an elevation of chemerin in the VAT after the ethanol treatment.

Lipotoxicity, a Potential Risk Factor for the Increasing Prevalence of Subclinical Hypothyroidism?

CONTEXT Subclinical hypothyroidism (SCH) is an important public health problem worldwide for its increasing prevalence and potential deleterious effects, whereas its etiology has not been fully elucidated. Lipotoxicity exerts extensive and serious impact on human health, but so far, the potential effect of lipotoxicity on thyroid is unclear. OBJECTIVE The objective of the study was to assess the association between serum triglyceride levels and the risk for SCH. DESIGN, PARTICIPANTS, AND METHODS We conducted a population-based case-control study. A total of 24 100 subjects with similar and stable iodine nutrition status were recruited from China. Cases of 5033 SCH patients were identified and equal controls were matched by age, gender, and region. Conditional logistic regression was used to analyze the association between serum triglyceride levels and risk for SCH. RESULTS Hypertriglyceridemia was associated with an approximately 35% increased risk for SCH in both men (odds ratio 1.325; 95% confidence interval 1.002-1.753) and women (odds ratio 1.397; 95% confidence interval 1.217-1.604), even after adjustment for potential confounders. Notably, the risk for SCH increased progressively following the elevation of serum triglyceride levels. Compared with individuals with serum triglyceride levels less than 0.97 mmol/L, the risk for SCH increased approximately 1.9-fold in men and 1.4-fold in women, respectively, when triglyceride levels were greater than 1.99 mmol/L. CONCLUSION Our findings suggested that hypertriglyceridemia was positively associated with the risk for SCH.

Identification and Functional Characterization of a Large Deletion of the CYP11B1 Gene Causing an 11β-Hydroxylase Deficiency in a Chinese Pedigree

Background: Steroid 11β-hydroxylase deficiency (11OHD) is the second most common cause of congenital adrenal hyperplasia. Inherited in an autosomal recessive manner, 11OHD is caused by mutations in the CYP11B1 gene. Objective: To identify the mutation causing 11OHD in a Chinese pedigree and analyze the functional consequences and phenotype associated with this mutation. Methods: A Chinese family with 11OHD was screened for mutations in the CYP11B1 gene. Mini-gene experiment was performed to mimic the natural splicing and outcome of the genetic variation. Results: Complete DNA sequencing of the CYP11B1 gene revealed a novel 449-bp homozygous deletion (g.2697del449) in the patient and a heterozygous deletion in both of the patient’s parents and sister. This mutation was predicted to lead to the skipping of part of exon 3 and all of exon 4 and inserting of part of intron 4 in the CYP11B1 mRNA. It generated a truncated protein and resulted in the complete destruction of the heme-binding domain of the enzyme. Conclusions: The novel deletion drastically affects normal protein structure and abolishes normal enzyme activity, leading to a severe phenotype of congenital adrenal hyperplasia due to 11OHD.

Benefits of Levothyroxine Replacement Therapy on Nonalcoholic Fatty Liver Disease in Subclinical Hypothyroidism Patients

Objectives. To evaluate the effect of levothyroxine (LT4) replacement therapy on nonalcoholic fatty liver disease (NAFLD) in subclinical hypothyroidism (SCH) patients. Methods. This study was a post hoc analysis of a randomized controlled trial and involved 33 significant and 330 mild SCH patients. All of the significant SCH patients received LT4 supplement. The mild SCH patients were grouped as LT4 treated or not. After 15 months of follow-up, prevalence of NAFLD in each group was reevaluated. Subgroup analysis was conducted in mild SCH patients with dyslipidemia. Results. After treatment with LT4, the prevalence of NAFLD in significant SCH patients reduced from 48.5% to 24.2% (p = 0.041). In mild SCH patients, prevalence of NAFLD and serum alanine aminotransferase (ALT) was not significantly affected by LT4 supplementation. Nonetheless, mild SCH patients with dyslipidemia who received LT4 treatment experienced decreases in the prevalence of NAFLD and serum ALT levels (p < 0.05 for both). In contrast, these parameters remained comparably stable in patients who were not treated. Conclusion. LT4 supplementation has benefits on NAFLD in significant SCH patients or mild SCH patients with dyslipidemia. For NAFLD patients with SCH, appropriate supplementation of LT4 may be an effective means of controlling NAFLD. The original trial was registered with ClinicalTrials.gov (NCT01848171).