A coupled finite-volume CFD solver for two-dimensional elasto-hydrodynamic lubrication problems with particular application to rolling element bearings

This paper describes a new computational fluid dynamics methodology for modelling elastohydrodynamic contacts. A finite-volume technique is implemented in the ‘OpenFOAM’ package to solve the Navier-Stokes equations and resolve all gradients in a lubricated rolling-sliding contact. The method fully accounts for fluid-solid interactions and is stable over a wide range of contact conditions, including pressures representative of practical rolling bearing and gear applications. The elastic deformation of the solid, fluid cavitation and compressibility, as well as thermal effects are accounted for. Results are presented for rolling-sliding line contacts of an elastic cylinder on a rigid flat to validate the model predictions, illustrate its capabilities, and identify some example conditions under which the traditional Reynolds-based predictions deviate from the full CFD solution

Effect of sugar-sweetened beverage taxation on sugars intake and dental caries : an umbrella review of a global perspective

Background As part of the Global Strategy on Oral health, the World Health Organization (WHO) is exploring cost-effective interventions for oral health, including taxation on sugar-sweetened beverages (SSBs). To inform this process, this umbrella review aimed to identify the best available estimates pertaining to the impact of SSB taxation on the reduction of sugars intake, and the sugars-caries dose–response, such that estimates of the impact of SSB taxation on averting dental caries in both high (HIC) and low and middle (LMIC) countries be available. Methods The questions addressed were: (1) what are the effects of SSB taxation on consumption of SSBs and (2) sugars? (3) What is the effect on caries of decreasing sugars? and (4) what is the likely impact of a 20% volumetric SSB tax on the number of active caries prevented over 10 years? Data sources included PubMed, Embase, Web of Science, Scopus, CINAHL, Dentistry and Oral Sciences Source, Cochrane Library, Joanna Briggs Institute (JBI) Systematic Review Register, and PROSPERO. The review was conducted with reference to JBI guidelines. The quality of included systematic reviews was assessed using AMSTAR to identify best evidence. Results From 419 systematic reviews identified for questions 1 & 2, and 103 for question 3, 48 (Questions 1 & 2) and 21 (Question 3) underwent full text screening, yielding 14 and five included reviews respectively. Best available data indicated a 10% tax would reduce SSB intake by 10.0% (95% CI: -5.0, 14.7%) in HIC and by 9% (range -6.0 to 12.0%) in LMIC, and that a 20% tax would reduce free sugars intake on average by 4.0 g/d in LMIC and 4.4 g/d in HIC. Based on best available dose response data, this could reduce the number of teeth with caries per adults (HIC and LMIC) by 0.03 and caries occurrence in children by 2.7% (LMIC) and 2.9% (HIC), over a 10-year period. Conclusion Best available data suggest a 20% volumetric SSB tax would have a modest impact on prevalence and severity of dental caries in both HIC and LMIC

Effects of intragastric administration of L-tryptophan on the glycaemic response to a nutrient drink in men with type 2 diabetes - impacts on gastric emptying, glucoregulatory hormones and glucose absorption

Published: 05 January 2021BACKGROUND: The rate of gastric emptying and glucoregulatory hormones are key determinants of postprandial glycaemia. Intragastric administration of L-tryptophan slows gastric emptying and reduces the glycaemic response to a nutrient drink in lean individuals and those with obesity. We investigated whether tryptophan decreases postprandial glycaemia and slows gastric emptying in type 2 diabetes (T2D). METHODS: Twelve men with T2D (age: 63 ± 2 years, HbA1c: 49.7 ± 2.5 mmol/mol, BMI: 30 ± 1 kg/m2) received, on three separate occasions, 3 g ('Trp-3') or 1.5 g ('Trp-1.5') tryptophan, or control (0.9% saline), intragastrically, in randomised, double-blind fashion, 30 min before a mixed-nutrient drink (500 kcal, 74 g carbohydrates), containing 3 g 3-O-methyl-D-glucose (3-OMG) to assess glucose absorption. Venous blood samples were obtained at baseline, after tryptophan, and for 2 h post-drink for measurements of plasma glucose, C-peptide, glucagon and 3-OMG. Gastric emptying of the drink was quantified using two-dimensional ultrasound. RESULTS: Tryptophan alone stimulated C-peptide (P = 0.002) and glucagon (P = 0.04), but did not affect fasting glucose. In response to the drink, Trp-3 lowered plasma glucose from t = 15-30 min and from t = 30-45 min compared with control and Trp-1.5, respectively (both P < 0.05), with no differences in peak glucose between treatments. Gastric emptying tended to be slower after Trp-3, but not Trp-1.5, than control (P = 0.06). Plasma C-peptide, glucagon and 3-OMG increased on all days, with no major differences between treatments. CONCLUSIONS: In people with T2D, intragastric administration of 3 g tryptophan modestly slows gastric emptying, associated with a delayed rise, but not an overall lowering of, postprandial glucose.Maryam Hajishafiee, Rachel A. Elovaris, Karen L. Jones, Leonie K. Heilbronn, Michael Horowitz, Sally D. Poppitt and Christine Feinle-Bisse

The effects of the amino acid, L-tryptophan, alone or with the fatty acid, lauric acid, on energy intake and postprandial glycaemia in health, obesity and type 2 diabetes

The studies reported in this thesis investigated whether specific dietary nutrients, including amino acids and fatty acids, when administered intraduodenally or intragastrically, reduce energy intake and/or blood glucose in healthy people and those with obesity and type 2 diabetes. These studies also investigated whether the effects are associated with modulation in GI functions, i.e. gut hormones, gut motility and gastric emptying. Moreover, they quantified extra-intestinal factors, including circulating amino acid concentrations, that may be surrogate markers for activity in central pathways in the brain. The key findings of the studies are: 1. Intragastric L-tryptophan, in a dose of 3 g, increased the plasma tryptophan/large neutral amino acids ratio more in lean participants than those with obesity, and in the lean the suppression of energy intake in response to tryptophan was related to the plasma tryptophan/LNAA ratio in the lean (Chapter 2). 2. Intragastric L-tryptophan, in a dose of 3 g, potently reduced energy intake, in both lean individuals and those with obesity. Suppression of energy intake was related to circulating tryptophan and the plasma tryptophan/LNAA ratio. L-tryptophan also suppressed appetite for 2 hours after the meal, despite the reduced energy intake. In the lean, appetite suppression was related to circulating tryptophan and the plasma tryptophan/LNAA ratio in lean participants (Chapter 3). 3. In individuals with type 2 diabetes, intragastric administration of L-tryptophan, in a dose of 3 g, before a carbohydrate-containing drink delayed the rise in plasma glucose, probably as a result of slowing of gastric emptying, but did not affect the overall blood glucose response (Chapter 4). 4. Intraduodenal infusion of lauric acid in combination with L-tryptophan, and lauric acid alone delayed the rise in postprandial plasma glucose in healthy men, probably by slowing of gastric emptying and GLP-1 stimulation, while L-tryptophan was ineffective (Chapter 5). In conclusion, the research presented in this thesis has established that while L-tryptophan potently suppresses energy intake in lean people and those with obesity, its effect on postprandial blood glucose differs between health, obesity and type 2 diabetes. GI factors, including gastric emptying and gut and pancreatic hormones, contribute to these effects, but apparently to varying extents, and other post-absorptive factors also play a role. Finally, the combination of lauric acid and L-tryptophan, each in doses that individually do not reduce postprandial glycaemia, has a potent effect to delay the early rise in postprandial glucose, reflecting slowing of gastric emptying. Further research is indicated to investigate the sustained effects of L-tryptophan on appetite, energy intake and body weight. Moreover, studies to assess the effect of the combination of lauric acid and L-tryptophan on postprandial glycaemia in obesity and/or type 2 diabetes are also indicated. Broadly, the purpose of these studies would be to determine whether these nutrients have the potential to offer a novel, nutrient-based treatment option for the management of obesity and/or type 2 diabetes.Thesis (Ph.D.) -- University of Adelaide, Adelaide Medical School, 202

Finite-volume CFD modelling of fluid-solid interaction in EHL contacts

Classically in an elastohydrodynamic (EHD) problem, the Reynolds equation is the most widely used PDE to describe the behaviour of lubricants in high-pressure non-conforming contacts, and elastic deformation is usually calculated using the Hertzian theory of elastic contacts. This thesis outlines the development of a new method for modelling of fluid-solid interactions in elastohydrodynamic lubrication (EHL) contact based on Finite Volume (FV) techniques. A Computational Fluid Dynamics (CFD) approach to solve the Navier-Stokes equations is implemented to model lubrication in roller bearings using the open-source package OpenFOAM. This has first been applied to simulate full film hydrodynamic lubrication (HL), enabling an accurate description of the flow within the entire domain surrounding the contact region. The rheology is assumed to be non-Newtonian and shear-thinning. The phenomenon of cavitation is modelled by implementing a homogenous equilibrium cavitation model, which maintains specified lubricant saturation pressure in cavitating region. The current fluid solver involves the solution of the full momentum and energy equations, and satisfying continuity. The aim is firstly to demonstrate the range of applicability and the limitations of traditional formulations of the Reynolds equation and secondly to highlight areas where Navier-Stokes based approaches are necessary for accurate solution of lubrication problems. Subsequently, a finite volume solid solver is fully coupled with the fluid solver in a forward iterative manner to take into account elastic deflection effects using Navier-Lamé equation. The advantage of using a single numerical tool enables an internal transfer of information at the fluid-solid interface through one common data structure. The stability of the model, in the presence of high contact pressures, is enhanced by incorporation of multigrid method, implicit coupling and improved mesh adaption and motion techniques. The developed model has been applied to a series of lubricated metal on metal smooth line contact with slide to roll ratios ranging from 0 to 2 and is stable for a wide range of industrial operating conditions (pressures up to 4 GPa). The model is further improved to account for time-dependent transient behaviour of an EHL rough contact. The results for a travelling ridge, dent and sinusoidal wave through EHL conjunction are presented.Open Acces

Gastrointestinal Sensing of Meal-Related Signals in Humans, and Dysregulations in Eating-Related Disorders

The upper gastrointestinal (GI) tract plays a critical role in sensing the arrival of a meal, including its volume as well as nutrient and non-nutrient contents. The presence of the meal in the stomach generates a mechanical distension signal, and, as gastric emptying progresses, nutrients increasingly interact with receptors on enteroendocrine cells, triggering the release of gut hormones, with lipid and protein being particularly potent. Collectively, these signals are transmitted to the brain to regulate appetite and energy intake, or in a feedback loop relayed back to the upper GI tract to further adjust GI functions, including gastric emptying. The research in this area to date has provided important insights into how sensing of intraluminal meal-related stimuli acutely regulates appetite and energy intake in humans. However, disturbances in the detection of these stimuli have been described in a number of eating-related disorders. This paper will review the GI sensing of meal-related stimuli and the relationship with appetite and energy intake, and examine changes in GI responses to luminal stimuli in obesity, functional dyspepsia and anorexia of ageing, as examples of eating-related disorders. A much better understanding of the mechanisms underlying these dysregulations is still required to assist in the development of effective management and treatment strategies in the future

Soy product consumption and association with health characteristics and dietary quality indices in Isfahan, Iran

BACKGROUND: To determine the average intake of soy products and its association with socio-demographic, general and health characteristics, and dietary quality indices among the population of Isfahan, Iran. METHODS: In this descriptive cross-sectional study conducted on 491 subjects in 2013-2014, grocery stores, nuts stores, chain stores, and supermarkets from different areas of Isfahan Municipality were visited. Shop owners were asked to report the amounts of soy products sales (soy nut, processed soy protein, soy milk and soy yogurt). Furthermore, a food frequency questionnaire was completed from 496 customers by an experienced nutritionist. Mean sales and intake of soy products and dietary intakes including dietary quality indices and mean adequacy ratio (MAR) as well as anthropometric and socio-demographic variables were assessed. RESULTS: Soy protein and soy yogurt are the highest [673 &plusmn; 81 (g/month)] and lowest [420 &plusmn; 148 (g/month)] purchased soy products, respectively. While soy nut [63 &plusmn; 10 (g/month)] was consumed to the lowest amount, soy protein [236 &plusmn; 39 (g/month)] was the most consumed soy product. Subjects with higher consumption of soy products were older and had higher intake of protein, vitamin C, zinc and iron, and lower intake of whole grains, legumes, and vegetables as well as greater values of MAR and dietary diversity score as well as nutrient adequacy ratio for vitamin C. CONCLUSION: Soy protein is the most purchased and consumed soy product among people living in Isfahan. More intakes of whole grains and vegetables among those with higher consumption of soy foods could define greater quantities of zinc, iron and vitamin C in the diet. Soy consumption had a reverse correlation with body mass index.&nbsp;</div

Effects of intraduodenal infusion of lauric acid and L-tryptophan, alone and combined, on glucoregulatory hormones, gastric emptying and glycaemia in healthy men

Background and aim: In healthy men, intraduodenal administration of the fatty acid, lauric acid (‘C12’) and the amino acid, L-tryptophan (‘TRP’), at loads that individually do not affect energy intake, reduce energy intake sub- stantially when combined. C12 and TRP may also stimulate cholecystokinin and glucagon-like peptide-1 (GLP-1), which both slow gastric emptying, a key determinant of postprandial blood glucose. Accordingly, combination of C12 and TRP has the potential to reduce post-meal glycaemia more than either nutrient alone. Methods: Twelve healthy, lean men (age (mean ± SD): 28 ± 7 years) received, on 4 separate occasions, 45-min intraduodenal infusions of C12 (0.3 kcal/min), TRP (0.1 kcal/min), C12 + TRP (0.4 kcal/min), or 0.9% saline (control), in a randomised, double-blind fashion. 30 min after commencement of the infusion a mixed- nutrient drink was consumed and gastric emptying measured (13C breath-test) for 3 h. Blood samples were obtained at baseline, in response to treatments alone, and for 2 h post-drink for measurements of plasma glucose, cholecystokinin, GLP-1, C-peptide, insulin and glucagon. ‘Early’ (first 30 min) and ‘overall’ glycaemic and hormone responses were evaluated. Results: C12 + TRP and C12 delayed the rise in, but did not affect the overall glycaemic response to the drink, compared with control and TRP (all P < 0.05). C12 + TRP slowed gastric emptying compared with control and TRP (both P < 0.005), and C12 non-significantly slowed gastric emptying compared with control (P = 0.090). C12 + TRP and C12 delayed the rise in C-peptide and insulin, and also stimulated CCK and glucagon, compared with control and TRP (all P < 0.05). Only C12 + TRP stimulated early and overall GLP-1 compared with control (P < 0.05). Conclusions: In healthy men, C12 + TRP and C12, in the loads administered, had comparable effects to delay the rise in glucose following a nutrient drink, probably primarily by slowing of gastric emptying, as a result of CCK and GLP-1 stimulation, while TRP had no effect.M. Hajishafiee, C. McVeay. K. Lange, J.F. Rehfeld, M. Horowitz, C. Feinle-Bisse