F. Van De Velde

Experimental verification of the mechanisms causing stick–slip motion originating from relative deceleration

Abstract In literature, the stick–slip phenomenon is usually explained from an initial stick-phase. The stability conditions with respect to stick–slip (the occurrence or not) are also derived by checking the reoccurrence of a relative standstill (stick-phase) after the slip-phase that has been following an initial stick-phase. However, stick–slip can also arise from an initial situation of pure slip. In this paper, it is experimentally shown that friction induced tangential oscillations during stick–slip can merge into stick–slip during an impressed deceleration, if their amplitude is sufficiently large. Owing to the interaction between friction phenomena and the dynamic behaviour of the mechanical system of which the friction interface is a part, the (negative) friction force–relative speed gradient (d F /d v rel ), which gives rise to the tangential oscillations and has to be considered for the study of stick–slip, must be derived from changes of the relative speed with the same time-constant as the mechanical system. It is also experimentally shown that the risk of stick–slip during deceleration is enhanced by an increase of the time-length of deceleration and by an increase of the tangential stiffness of the mechanical system. The correlation of the experimental results with previous theoretical analysis is clarified. As a result, some widely accepted models for the friction as a function of the relative speed have to be put in question. It is also shown that the major problem in determining the gradient d F /d v rel is the inadequateness of the classical friction test rigs.

Serum vascular cell adhesion molecule-1 predicts significant liver fibrosis in non-alcoholic fatty liver disease

Background:Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide and is strongly associated with obesity, dyslipidemia and insulin resistance. NAFLD often presents as simple steatosis (NAFL) but can progress to non-alcoholic steatohepatitis (NASH) and fibrosis. Current non-invasive biomarkers are not tailored to identify significant (⩾F2) fibrosis, although recent guidelines recommend a stringent follow-up of this patient population. We and others have reported on the role of pathological angiogenesis in the pathogenesis of NAFLD, highlighting pro-angiogenic factors as potential diagnostic markers.Objective:To investigate the applicability of angiogenic and endothelial dysfunction markers as non-invasive diagnostic tools for NASH or NASH-associated fibrosis in obese patients.Methods:In a prospective cross-sectional study, male patients undergoing bariatric surgery (n=61) and control patients (n=35) were recruited. Serum protein levels and visceral adipose tissue gene expression of endothelial dysfunction and angiogenic markers were analyzed by multiplex bead-based assay and quantitative RT-PCR, respectively. For validation, we recruited a second cohort of patients undergoing bariatric surgery (n=40) and a cohort of NAFLD patients from our outpatient clinic (n=30).Results:We identified serum vascular cell adhesion molecule-1 (VCAM-1) as an independent predictor for ⩾F2 fibrosis (median 14.0 vs 8.7 ng ml−1 in patients with and without significant fibrosis; P<0.0001) with an area under the receiver-operating characteristics (AUROC) curve of 0.80. The cutoff point of 13.2 ng ml−1 showed a sensitivity of 80% and specificity of 83%. In line with these results, VCAM-1 visceral adipose tissue gene expression was also elevated in patients with fibrosis (P=0.030). In the bariatric surgery and clinical validation cohorts, VCAM-1 displayed similar AUROCs of 0.89 and 0.85, respectively.Conclusions:VCAM-1 levels are able to accurately predict significant (⩾F2) fibrosis in NAFLD patients.

Substitution of Inexpensive Bench Tests for the FZG Scuffing Test—Part II: Oil Tests©

The standardized FZG apparatus is widely applied for assessing the anti-scuffing properties of gear lubricants. However, this rest is very time-consuming and expensive. For the development of new transmission lubricants, quicker and less expensive tests would be useful. In this two-part article, the possibility to qualify gear lubricants by means of two common bench tests (SRV Optimol and four-ball) was investigated. In the first part, the different test rigs (FZG, SRV, four-ball) are presented and the parameters related to scuffing according to literature (lubricant film thickness, flash temperature and contact pressure) are calculated for the three testers. In this part, test results of eight lubricants obtained with the three test rigs are presented and compared. Results showed a.o. that the SRV wear scar diameter and the four-ball load-wear index correlated with the FZG failure load stage. Inconsistencies between test results are clarified based on lubricant composition and the parameters related to s...

Substitution of Inexpensive Bench Tests for the FZG Scuffing Test—Part I: Calculations

The standardized FZG apparatus is widely applied for assessing the anti-scuffing properties of gear lubricants. However, this test is very time-consuming and expensive. For the development of new transmission lubricants, quicker and less expensive tests would be useful. In this two-part article, the possibility to qualify gear lubricants by means of two common bench tests (SRV Optimol and four-ball) was investigated. In the first part, the different test rigs (FZG, SRV, four-ball) are presented and the parameters related to scuffing according to literature (lubricant film thickness, flash temperature and contact pressure) are calculated for the three testers. In the second part, test results of eight lubricants obtained with the three test rigs are presented and compared. Results showed a.o. that the SRV wear scar diameter and the four-ball load-wear index correlated with the FZG failure load stage. Inconsistencies between test results are clarified based on lubricant composition and the parameters relate...

Reproducibility and least significant differences of oral glucose tolerance test-derived parameters in a postmenopausal population without diabetes

Diabetes & Metabolism - In Press.Proof corrected by the author Available online since mercredi 18 janvier 2017